Fruit quality and production of cactus pear (Opuntiaspp.) fruit clones selected for increased frost hardiness

Journal of Arid Environments (1997) 37: 123–143

Fruit quality and production of cactus pear (Opuntia spp.) fruit clones selected for increased frost hardiness

John Parish & Peter Felker Center for Semi-Arid Forest Resources, Caesar Kleberg Wildlife Institute, Texas A&M University, Campus Box 218, Kingsville, TX 78363, U.S.A. (Received 2 December 1996, accepted 1 February 1997) The principal limitation to cultivation of cactus for fruit in the south-western United States is lack of hardiness to freezing weather. This field trial compared 22 Opuntia clones selected for increased cold hardiness, fruit yield, and fruit quality, i.e. pH, sugar content and seed content. Mexican accessions 1380, 1277, 1281 and 1300 had the highest yields averaging between 2·5 and 5·2 kg m–2 while the Chilean clones had lower yields, yet greater sugar content and generally lower seed contents. As there is considerable aversion by first time consumers of cactus pears to seed size and number, we evaluated seed number, seed weight per fruit and weight per seed. Our trial found a considerable range in seed weight from 2·19 to 6·37 g fruit –1. While the Chilean varieties had among the lowest seed weight per fruit (2·2 g fruit–1) and were similar in seed weight to the recently reported BS1 parthenocarpic clones in Israel, a few Mexican varieties were comparable. In summary, Chilean varieties were most promising for high sugar content and low seed weight per fruit. Mexican varieties with high yields did not contain high sugar. ©1997 Academic Press Limited Keywords: arid; desertification; fruit; cactus pear; Latin America; Opuntia

Introduction Cactus pear (Opuntia spp.) is in the Cactaceae family and is native to arid and semiarid regions of the western hemisphere (Benson, 1982). The success of Opuntia in these areas has been attributed to its CAM metabolism (Kluge & Ting, 1978) which promotes high drought resistance and high water-use efficiency. Such efficient conservation of water in times of drought has caused it to be widely used as an emergency livestock feed (Griffiths, 1905). Also its tender young pads, known as ‘nopalitos’, are used in Mexico and south Texas as a green vegetable (Russell & Felker, 1987). Many Opuntia species, known as ‘tuna’ in Mexico, produce sweet edible fruit (Griffiths & Hare, 1907). While the cultivation of Opuntia for fruit production in Mexico is widespread 0140–1963/97/010123 + 21 $25.00/0/ae970261

© 1997 Academic Press Limited

124

J. PARISH & P. FELKER

(Mondragon & Perez, 1994; Pimienta 1994), the exploitation of this resource for fruit production in Texas is non-existent. The major limitation to cultivation of cactus in the south-western United States, excluding California (Curtis, 1977), is hardiness to freezing weather (Griffiths, 1915; Uphof, 1916). As of yet there is no commercial fruiting variety of Opuntia that can withstand the seasonally intermittent freezes that occur in south Texas (Gregory et al., 1993). When temperatures in a Texas field trial dropped to –12°C in 1989, the native spiny O. lindheimeri Engelm. and the spineless O. ellisiana Griffiths were not damaged (Gregory et al., 1993). However, all clones from Mexico, Chile, Brazil, South Africa and Algeria froze to ground level. Since then additional collections have been made to improve the genetic diversity of coldhardy fruit-producing Opuntia clones in our field site (Barrientos et al., 1992). We were fortunate enough to obtain selections from the Universidad Autonoma Agraria Antonio Narro (UAAAN) Germplasm at Saltillo where scientists have been conducting research on cold hardy Opuntia fruit since the 1960s (Martinez, 1968; Borrego-Escalante et al., 1990; Barrientos et al., 1992). Some of the selections originated from breeding materials that had survived a freeze of –16°C in 1962 in Saltillo without damage (Barrientos et al., 1992). Other collections were made from the Sierra Madras at 2300 m elevation near Saltillo where villagers stated temperatures often reached –12°C. Along with the need to increase cold hardiness is the importance to select for fruit quality. Principal factors affecting fruit quality in cactus pear include sugar content, peel color, fresh weight, pulp weight, and seed content (Cantwell, 1991). Many popular cultivars in Mexico vary greatly in color, exceed 120 g fruit–1 and average between 12 and 17% sugar (Pimienta, 1994). This differs considerably from the Texas native O. lindheimeri which produces small purple seedy fruits averaging about 40 g with only 8% sugar (Russell & Felker, 1987). Collections in this trial included fruit from O. ficus-indica (L.) Mill., O. megacantha Salm-Dyck, O. hyptiacantha Weber, O. streptacantha Lem., O. inermis DC., and O. crassa Haw. As there is considerable aversion by first time consumers of cactus pears to seed size and number, reducing seediness is a major objective for the enhancement of its commercialization (Caplan, 1995). Studies by Pimienta & Engleman (1985) have reported that the principal pulp parts in cactus pear develop from the dorsal epidermis of the funicular envelope, thus a reduced seed number may in turn reduce pulp weight. However, Pimienta & Engelman (1985) suggested that seediness might be reduced through the production of aborted seeds. With five growing seasons since the establishment of newer cold hardy material from Saltillo, the clones in this trial have approached commercial production levels. Thus, the objective of this study was to compare fruit quality and production, at commercial production levels, of the newer cold hardy material to more standard clones from Chile, Brazil, and central Mexico.

Materials and methods Experimental design For fruit analysis, ten 5-year-old plants in Kingsville, Texas ranging from 3 to 5 m in height were used. The ten plants were located in two, five plant row-plots with a 1 m inter-row and a 4 m between-row spacing. For the purposes of fruit characterization, individual fruits were considered as replicates. Twelve to 18 fruits were collected from the two, five plant row-plots with no less than five fruits harvested from a row-plot. While there were 70 accessions in this trial, only 22 accessions from Brazil, Chile and Mexico produced sufficient fruit in both row-plots for analysis. The accessions were

OPUNTIA FRUIT FROST HARDINESS

125

evaluated for fruit yield, mean sugar content, mean fresh weight, mean pulp weight, mean seed number, mean seed weight per fruit and mean weight per seed. For yield estimations, the entire row-plot was considered as a replicate and thus there were only two replications for the yield estimates. The row-plots were arranged in a randomized complete block design. As these plants did not have guard rows, the production per m2 estimates are greater than could be expected in commercial production. Nevertheless these yields can be used to compare the accessions and provide an estimate of general productivity. We also tested for significant (p < 0·10) general linear and quadratic relationships between easily measurable fruit morphological characteristics and sugar content to determine which morphological measurements would be most useful in predicting fruit maturity. Quadratic relationships were considered to be significant (p < 0·10) only if the coefficient of the quadratic term was significant (p < 0·10). The morphological variables used for these general linear regression analyses were fruit scar depth, fruit scar diameter, fresh weight, pulp weight, peel weight and pH.

Fruit collection and analysis After measuring the picked fruit height, the color of each fruit was graded according to the Royal Horticultural Society Colour Chart. Fruits were stored and refrigerated in paper bags for no more than 24 h before analysis. Each fruit was measured for length, width, scar depth, scar diameter, fresh weight and pulp weight. Each fruit pulp was blended in a kitchen blender and subjected to vacuum filtration (Fisherbrand P8) to extract juice for sugar content and pH analysis. Sugar content was measured with a Reichert-Jung temperature compensated hand refractometer (model 10430) calibrated using an 8–15% glucose solution. Peel weights were determined by subtracting pulp weights from fresh weights. Four blended pulps for each accession (two pulps from each block) were strained through a fine mesh screen to capture seeds, which were then air-dried, counted, and weighed. Weight per seed was determined by dividing the total weight of seeds for the four pulps by the total number of seeds.

Fruit yield Fruit yield for each accession was determined by counting all fruits on the five plants in each of the two replicates at the end of each month. The number of fruits per five plants in the highest yielding month was multiplied by the estimated mean fresh weight per fruit at harvest in July or August 1995, and 2500 plant ha–1 population density to obtain estimated fruit yield in kg m–2 ( = 0·1 (ton ha–1)).

Soils Two soil series, Hidalgo and Palobia, occurred in these plots (USDA, 1975). Hidalgo is most extensively distributed. This series is taxonomically identified as a member of fine loamy mixed hyperthermic family of Typic Calcuistolls (USDA, 1978). These soils lack a fluctuating ground-water table in their deep layers. They are well-drained, have slow runoff, and are moderately permeable. They have high inherent fertility and high production potentials. Mean values for five soil samples were organic matter 0·5%, pH 6·5 and nitrate N 3 mg kg–1. A total of 100 kg N ha–1, 100 kg P ha–1 and 100 kg K ha–1 was applied to the soil surface within 0·5 m of the plants in the winter of 1994–95.

126

J. PARISH & P. FELKER

Table 1. Mean yield and frost scores, color, and presence of thorns for cactus pears harvested in the summer of 1995 in Kingsville, Texas

Species, Yield, Acc.#, origin and kg m–2† UAAAN code* (mean±S.D.)

Royal Horticultural Society Color Chart Code‡

Frost score§

Thorns¶ (+/–)

na

–

80±13

–

47±0

–

52±16

–

57±23

–

na

–

38±18

–

na

+

na

+

26±6

+

na

+

na

–

na

+

O. megacantha 1380 Mexico AN-V5 O. ficus-indica 1277 Mexico

5·2±2·6

Y-O grp. 22A

4·1±0·41

O. streptacantha 1281 Mexico

3·0±0·56

O. ficus-indica 1300 Mexico O. ficus-indica 1320 Chile

2·5±3·4

O. ficus-indica 1278 Mexico O. inermis 1270 Brazil Opuntia sp. 1393 Mexico O. megacantha 1383 Mexico AN-T3 O. hyptiacantha 1287 Mexico O. megacantha 1297 Mexico O. ficus-indica 1294 Mexico O. ficus-indica 1376 Mexico AN-V1 O. megacantha 1390 Mexico AN-TV6 O. ficus-indica 1319 Chile Opuntia sp. 1392 Mexico O. ficus-indica 1279 Mexico O. ficus-indica 1282 Mexico O. ficus-indica 1301 Mexico

1·8±2·1

Y grp. 22A Y grp. 26A Y grp. 6B R grp. 50B R grp. 46C R grp. 47C R-P grp. 59A V grp. 86A Y-Gn grp. 152D Y-O grp. 22A Y-O grp. 20A Y grp. 11A Y grp. 5B Y grp. 153 D O grp. 26B Y-Gn grp. 151A Y-Gn grp. 154A Y-Gn grp. 145C Y grp. 4C Y-Gn grp. 154C Y grp. 11A O grp. 26A Y-Gn grp. 150C Y-Gn grp. 154C O grp. 26B Y-O grp. 26B Gn-Y grp. 1B Y-Gn grp. 153D

2·1±0·19

1·6±0·71 1·4±1·6 1·3±0·38 1·2±0·24 1·0±0·91 1·0±0·72 0·87±0·25 0·74±0·26

Y-Gn grp. 154C Y-Gn grp. 150C

na

–

0·70±0·30

Y-Gn grp. 153C

28±14

–

0·65±0·070

Gy-R grp. 179A R grp. 40C V grp. 86A

na

–

na

–

na

–

56±19

–

0·56±0·18 0·44±0·32 0·43±0·42

P-V grp. 80A R-P grp. 60B R grp. 50C Gy-R grp. 34A

OPUNTIA FRUIT FROST HARDINESS

127

Table 1. (continued)

Species, Yield, Acc.#, origin and kg m–2† UAAAN code* (mean±S.D.) O. crassa 1379 Mexico AN-V4 Opuntia sp. 1398 Mexico O. ficus-indica 1321 Chile

0·22±0·21 0·20±0·097 0·15±0·087

Royal Horticultural Society Color Chart Code‡ Gy-R grp. 179B R grp. 42A R grp. 47A Y-Gn grp. 151B Y-O grp. 17D Gy-O grp. 163C Y-Gn grp. 144B

Frost score§

Thorns¶ (+/–)

na

–

na

+

88±11

–

*Designation of clone by Universidad Autonoma Agraria Antonio Narro. †Standard deviation, N=2. ‡Y=yellow; Gn=green; O=orange; R=red; P=purple; V=violet; Gy=greyed; grp.=group. §Frost score is estimate of % above-ground height remaining after freeze of 1990 (Gregory et al., 1993); na=frost score unknown. ¶+=thorns present; –=thorns absent.

Climate The climate of Kingsville is semi-arid and subtropical. Mean maximum temperatures exceeded 30°C from May through October for 1961–1990. Mean monthly minimum temperatures dropped below 10°C from December through February for 1961–1990. Mean minimum temperatures were 8°C for December, 7°C for January and 9°C for February (National Oceanic and Atmospheric Association (NOAA), 1992). Frost scores reported here were taken from Gregory et al. (1993). As a severe freeze has not occurred since 1991, after which many new clones were obtained, frost scores were not available for many new accessions. Mean annual precipitation in Kingsville from 1961 to 1990 was 690 mm (NOAA, 1992). Rainfall in 1995 however was higher than usual at 864 mm with a peak in August of 198 mm (Kingsville Record and Bishop News, 1996). Results Fruit production Mexican varieties were among the greatest fruit producers with yellow-fruited accession 1380 (AN-V5) ranking highest with a mean yield of 5·2 kg m–2 (Table 1). Accession 1277 from Milpa Alta, Mexico was second with a mean yield of 4·1 kg m–2 and second highest in frost score at 80% (Gregory et al., 1993). Although third ranking accession 1281 from Chapingo, Mexico, with a mean yield of 3·0 kg m–2 had a much lower frost score of 47% (Gregory et al., 1993), its red fruit was unique among the high fruit yielding clones in our study. The fourth ranking accession 1300, from Chapingo, Mexico had a mean yield of 2·5 kg m–2. Overall, fruit yields were very variable averaging between 0·15 and 5·2 kg m–2. Yields for Chilean clones averaged between 0·15 and 2·1 kg m–2. Accession 1270, the only Brazilian clone, ranked seventh in yield with a mean of 1·6 kg m–2 The top seven fruit yielding cacti were spineless. Eight of the top ten fruit yielding varieties were yellow as graded by the Royal Horticultural Society colour chart. Chilean variety 1320 was the highest yielding of the Brazilian and Chilean clones in mean fruit production, ranking fifth with 2·1 kg m–2. While Chilean

128

J. PARISH & P. FELKER

accession 1321 ranked highest in frost score at 88% (Gregory et al., 1993), it had the lowest mean yield of 0·15 kg m–2.

Sugar content The Chilean varieties 1319 and 1321 had the greatest mean sugar content at 14·6% and 13·8%, respectively (Table 2). Accession 1383 (AN-T3) had the greatest mean sugar content of the Mexican clones and ranked third overall at 13·4%. Sugar content for fruits in this study averaged between 10·7 and 14·6%. Half of the top ranking Mexican varieties for mean sugar content were collected from Chapingo. Accession 1320 was the lowest ranking Chilean variety in mean sugar content at 12·3% and was higher than the only Brazilian clone, 1270, at 11·9% sugar. Accession 1376 (AN-V1) from Mexico ranked lowest in mean sugar content at 10·7%.

Fresh weight The largest fruits in the trial were from Mexican accession 1287 and Chilean accession 1320 averaging 160 and 151 g, respectively (Table 2). The thorny yellow-fruited Mexican accession 1398 from Los Llanos ranked third in mean fresh weight at 148 g. Out of the 22 accessions in this trial, 17 produced individual fruits averaging between 120 and 160 g. Fresh weights overall averaged between 113 and 160 g. Fresh weights for Chilean accessions averaged between 120 and 151 g. Brazilian clone 1270 had relatively low mean fresh weight of 121 g. Chilean clone 1321 was the lowest ranked variety among Chilean and Brazilian accessions in mean fresh weight at 120 g. Overall, accession 1376 (AN-V1) was the lowest ranked variety in mean fresh weight at 113 g.

pH Mexican varieties 1398 and 1383 (AN-T3) ranked the lowest in fruit pH at 5·6 and 5·8, respectively (Table 2). Chilean accession 1320 had the lowest pH of Chilean and Brazilian varieties at 5·9. The only Brazilian clone 1270 ranked fourth in lowest pH at 6·0. The pH of fruit in the trial ranged between 5·6 and 6·5. The pH for Chilean varieties ranged between 5·9 and 6·3. Yellow-fruited thornless variety 1278 from Chapingo ranked the highest in pH at 6·5.

Pulp and peel weight The Chilean varieties varied greatly in mean pulp weight, with accession 1320 ranking highest at 81 g, and 1319 ranking next to last at 48 g (Table 2). Accession 1297 from Chapingo was the highest ranking Mexican variety in mean pulp weight at 79 g. The mean pulp weight of the only Brazilian clone 1270 ranked ninth at 69 g. Thornless purple-fruited Mexican variety 1282 from Chapingo ranked last in mean pulp weight at 47·5 g. Mexican varieties 1398 and 1287 ranked the highest in mean peel weight at 88 and 84 g, respectively (Table 2). Mexican accessions 1278 from Chapingo and 1390 from Saltillo had the lowest mean peel weight in the study at 41 and 44 g, respectively. Brazilian clone 1270 ranked third in lowest mean peel weight at 53 g. While peel weights overall averaged between 41 and 88 g, Chilean peel weights were roughly similar, averaging between 67 and 76 g.

OPUNTIA FRUIT FROST HARDINESS

129

Fruit seed measurements Mexican and Chilean varieties shared the top four rankings in lowest mean seed weight per fruit, with accession 1282 and 1279 from Mexico being first and third at 2·19 g fruit–1 and 2·27 g fruit–1, and accessions 1319 and 1321 from Chile being second and fourth at 2·21 and 2·30 g fruit–1, respectively (Table 3). However, the other Chilean variety 1320 was ranked near last in lowest mean seed weight per fruit at 4·63 g. Brazilian clone 1270 was ranked fourteenth in lowest mean seed weight per fruit at 3·54 g. Seed weight per fruit averaged between 2·19 and 6·37 g. Accession 1393 from Saltillo ranked last in lowest mean seed weight per fruit at 6·37 g. Chilean accession 1319 and Mexican accessions 1282 and 1380 had the lowest mean weight per seed at 10, 11 and 11 mg, respectively (Table 3). Two accessions from Chapingo, Mexico, 1278 and 1300, and one from UAAAN, accession 1390 (AN-TV6), ranked next in lowest mean weight per seed at 12 mg. Chilean variety 1321, Mexican variety 1277 and the only Brazilian clone, 1270, ranked next in lowest mean weight per seed at 13 mg. The weight per seed in this trial averaged between 10 and 21 mg. The weight per seed for Chilean fruit averaged between 10 and 14 mg. Mexican accessions 1376 (AN-V1) and 1393 ranked last in lowest mean weight per seed at 21 mg. Mexican accession 1279 from Chapingo had the lowest mean seed number at 144 seed fruit–1 (Table 3). Of the four clones producing fruit averaging less than 200 seeds fruit–1, accession 1321 from Chile ranked second at 174 seeds fruit–1. Other clones averaging less than 200 seeds fruit–1 were Mexican accessions 1392 and 1287 at 186 and 191, respectively. Brazilian clone 1270 was among the most seedy, averaging 279 seeds fruit–1. Chilean clone 1320 was the most seedy averaging 342 seeds fruit–1. Generally, fruits with the lowest mean seed weight per fruit also had a lower mean weight per seed and/or a lower mean seed number per fruit (Table 3). This was true for Chilean accession 1321 which ranked fourth in lowest mean seed weight per fruit at 2·3 g, seventh in lowest mean weight per seed at 13 mg, and second in lowest mean seed number at 174 seeds fruit–1. Another Chilean variety, 1319, ranked second in lowest mean seed weight per fruit at 2·21 g, first in lowest mean weight per seed at 10 mg, and yet ranked only eleventh in lowest mean seed number at 226 seeds fruit–1. Some Mexican varieties also showed this trend with accession 1282 ranking first in lowest mean seed weight per fruit at 2·19 g and second in lowest mean weight per seed at 11 mg, and sixth in lowest mean seed number at 204 seeds fruit–1. Mexican accession 1279, which ranked fourth in lowest mean seed weight per fruit at 2·27 g, ranked only fifteenth in lowest mean weight per seed at 16 mg, and yet ranked first in lowest mean seed number at 144 seeds fruit–1. There also appeared to be a relationship between high peel/pulp ratio and low mean seed weight per fruit. Five of the top six accessions in lowest mean seed weight per fruit possessed peel/pulp ratios greater than one, as was the case for Mexican varieties 1282, 1279, and 1287 and Chilean varieties 1319 and 1321. Chilean variety 1319 had the highest peel/pulp ratio of 1·57 while Mexican variety 1278 had the lowest of 0·56. Nine of the 22 varieties in the trial possessed peel/pulp ratios greater than one. Purplefruited thornless variety 1300, from Chapingo, produced fruits with peel/pulp ratios closest to one at 0·97. Accession 1300 was also the only variety to rank within the top three in both lowest mean peel and lowest mean pulp weight at 79 g and 77 g, respectively.

Morphological characters Chilean and Mexican accessions 1320 and 1300 shared top rankings in highest mean fruit width at 6·0 cm (Table 3). While accession 1287 was third in highest mean fruit

130

J. PARISH & P. FELKER

Table 2. Mean sugar content, fresh weight, pulp weight, peel weight and median pH for cactus pears harvested in the summer of 1995 in Kingsville, Texas

Species Acc. #, Fruit Origin and number UAAAN code* (N) O. ficus-indica 1319 Chile O. ficus-indica 1321 Chile O. megacantha 1383 Mexico AN-T3 O. ficus-idica 1294 Mexico O. ficus-indica 1278 Mexico O. megacantha 1390 Mexico AN-TV6 O. ficus-indica 1279 Mexico O. megacantha 1297 Mexico O. hypticantha 1287 Mexico O. streptacantha 1281 Mexico O. ficus-indica 1320 Chile O. inermis 1270 Brazil Opuntia sp. 1392 Mexico O. ficus-indica 1282 Mexico Opuntia sp. 1393 Mexico O. ficus-indica 1277 Mexico O. ficus-indica 1300 Mexico O. ficus-indica 1301 Mexico O. megacantha 1380 Mexico AN-V5 O. crassa 1379 Mexico AN-V4

Sugar (%)†

Fresh weight (g)†

Pulp weight (g)†

Peel weight (g)†

pH†

12

14·6±0·7

124·2±18·7

48·3±10·1

75·9±9·7

6·3±0·2

13

13·8±0·7

120·0±16·6

53·2±7·2

66·8±12·4 6·3±0·0

14

13·4±0·4

132·1±11·4

71·6±9·3

60·1±4·5

5·8±0·0

13

13·1±0·7

125·9±21·1

67·8±11·8

58·2±9·8

6·2±0·0

18

12·9±0·4

114·4±12·7

73·4±7·4

41·0±5·9

6·5±0·0

14

12·8±0·4

117·4±14·3

73·6±10·4

43·9±4·1

6·3±0·0

13

12·8±0·7

134·4±21·1

57·8±10·5

76·5±11·8 6·3±0·0

14

12·7±0·4

140·1±15·1

79·2±10·2

60·9±8·2

13

12·6±0·7

160·3±22·4

76·0±13·1

84·2±11·5 6·3±0·0

14

12·5±0·4

135·3±9·9

70·7±6·5

64·6±5·2

6·2±0·0

14

12·3±0·6

151·5±12·1

81·1±7·3

70·3±6·5

5·9±0·0

13

11·9±0·7

121·2±10·5

68·7±7·2

52·5±5·0

6·0±0·0

13

11·8±0·7

127·8±10·5

65·2±7·0

62·6±4·6

6·2±0·0

12

11·6±0·4

121·2±17·2

47·5±8·8

73·7±9·9

6·2±0·0

12

11·5±0·7

114·3±18·9

60·3±10·8

54·1±9·2

6·2±0·2

16

11·5±1·1

139·3±13·0

76·4±12·1

62·8±6·6

6·2±0·0

14

11·4±0·4

148·4±21·6

78·9±21·2

76·6±11·0 6·2±0·2

12

11·3±0·4

116·1±14·7

56·2±9·5

59·4±6·2

6·3±0·0

14

11·1±0·9

131·5±10·6

78·1±13·2

60·7±4·8

6·3±0·0

12

11·0±0·4

129·5±11·4

60·3±5·7

69·2±9·2

6·3±0·0

6·0±0·2

OPUNTIA FRUIT FROST HARDINESS

131

Table 2. (continued)

Species Acc. #, Fruit Origin and number UAAAN code* (N) Opuntia sp. 1398 Mexico O. ficus-indica 1376 Mexico AN-V1

Sugar (%)†

Fresh weight (g)†

Pulp weight (g)†

Peel weight (g)†

15

10·9±0·6

148·7±29·2

61·2±11·6

87·5±19·3 5·6±0·2

13

10·7±1·1

112·9±19·6

53·2±11·1

64·3±13·1 6·0±0·2

pH†

*Designation of clone by Universidad Autonoma Agraria Antonio Narro. †95% confidence interval.

width at 5·9 cm, it was first in highest mean fruit length at 11·1 cm and also had the highest mean fresh weight at 160 g. The second highest mean fruit length was for Mexican accession 1398 at 10·1 cm. Chilean accession 1320 had the highest mean fruit length of all the Chilean and Brazilian varieties at 9·3 cm. The only Brazilian clone, 1270, had a relatively low mean fruit length at 8·1 cm. Mexican accessions 1376 (AN-V1) and 1393 had the lowest mean fruit lengths at 7·3 cm. Mexican accessions 1278 and 1390 (AN-TV6) had the lowest mean fruit widths at 5·2 and 5·3 cm, respectively. The lowest mean fruit scar diameters were for Mexican accessions 1278 and 1390 (AN-TV6) at 18·4 and 19·5 mm, respectively (Table 3). Chilean accessions had relatively high fruit scar diameters, averaging between 24·5 and 28·2 mm. However, the highest mean fruit scar diameter belonged to Mexican variety 1297 at 28·5 mm. While 1297 had the highest mean fruit scar diameter, it also had the lowest mean fruit scar depth at 0·8 mm (Table 3). Accessions from UAAAN, 1376 (AN-V1) and 1383 (AN-T3) ranked second and third in lowest mean fruit scar depth at 2·1 mm and 2·5 mm, respectively. The four clones with the lowest mean fruit scar depths were spiny and produced yellow–green fruit. While overall fruit scar depth in the trial averaged between 0·8 and 8·5 mm, scar depth for South American clones averaged between 4·4 and 6·6 mm. UAAAN accession 1390 (AN-TV6) had the highest mean fruit scar depth at 8·5 mm. Relationships between fruit length, width and floral scar measurements and fruit sugar In an effort to develop quantitative maturity indices, we examined relationships between easily measurable fruit morphological characters and sugar content. Cantwell (1991) suggested that fruit maturity was associated with the filling in of the fruit scar (receptacle) to form a nearly flat surface. Thus, we included fruit scar depth and width measurements. To examine which external morphological measurements would be most useful in predicting fruit maturity, as judged by sugar content, we report p-values for significant (p < 0·10) linear regression relationships and significant (p < 0·10) quadratic coefficients (Table 4). Twelve of the 22 varieties in the trial had some significant (p < 0·10) morphological relationship with sugar content. As only one accession had a significant (p < 0·10) quadratic coefficient for scar depth and sugar content as compared to six accessions which had significant (p < 0·10) quadratic coefficients for scar diameter, scar depth is a less useful morphological character in predicting fruit maturity than scar diameter. Of the six accessions, 1282, 1287, 1297, 1301, 1319 and 1380 (AN-V5), that had

11 10 16 13 11 15 15 17 12 12 12 16

2·19±1·81

2·21±1·69

2·27±0·89

2·30±0·51

2·79±0·80

2·95±1·28

3·00±1·62

3·12±1·43

3·18±0·57

3·23±0·22

3·27±1·02

3·29±1·72

O. ficus-indica 1282 Mexico O. ficus-indica 1319 Chile O. ficus-indica 1279 Mexico O. ficus-indica 1321 Chile O. megacantha 1380 Mexico AN-V5 O. hyptiacantha 1287 Mexico O. ficus-indica 1294 Mexico Opuntia sp. 1392 Mexico O. megacantha 1390 Mexico AN-TV6 O. ficus-indica 1278 Mexico O. ficus-indica 1300 Mexico O. streptacantha 1281 Mexico

Weight per seed (mg)

Seed weight per fruit†‡ (g)

Species Acc. #, Origin and UAAAN code*

201±75

276±94

276±81

274±56

186±72

206±78

191±75

248±42

174±42

144±50

226±138

204±178

Seed no. per fruit†‡ (g)

5·6±0·2

6·0±0·2

5·2±0·2

5·3±0·2

5·8±0·2

5·6±0·4

5·9±0·4

5·7±0·2

5·6±0·2

5·8±0·4

5·7±0·4

5·5±0·2

Fruit width† (cm)

8·8±0·6

9·3±0·4

9·2±0·2

9·2±0·6

8·1±0·2

7·8±0·9

11·1±0·7

8·4±0·4

7·8±0·7

9·5±0·9

7·9±0·7

9·3±0·7

Fruit length† (cm)

21·9±1·9

24·4±2·2

18·4±1·1

19·5±0·9

23·8±1·1

23·0±1·3

22·4±2·4

21·6±1·3

28·2±2·0

22·2±1·3

26·9±3·1

24·0±1·3

Scar diam.† (mm)

Scar depth† (mm)

6·5±0·9

4·6±1·1

7·1±0·6

8·5±0·6

5·0±0·9

6·0±1·3

7·5±0·7

5·6±0·6

4·8±0·9

6·7±1·3

4·4±0·9

8·1±1·8

Table 3. Length, width, scar depth, scar diameter and seed content of cactus pears harvested in the summer of 1995 in Kingsville, Texas

132 J. PARISH & P. FELKER

13 17 14 17 13 14 14 21 21

3·54±0·64

3·64±1·60

3·68±0·80

3·68±2·22

3·92±1·14

4·31±1·18

4·63±1·21

5·59±3·47

6·37±4·26

310±180

268±136

342±72

304±56

296±69

211±136

257±78

212±69

279±47

213±111

Seed no. per fruit†‡ (g)

*Designation of clone by Universidad Autonoma Agraria Antonio Narro. †N =4. ‡95% confidence interval.

16

3·33±2·10

O. ficus-indica 1301 Mexico O. inermis 1270 Brazil O. crassa 1379 Mexico AN-V4 O. megacantha 1383 Mexico AN-T3 Opuntia sp. 1398 Mexico O. ficus-indica 1277 Mexico O. megacantha 1297 Mexico O. ficus-indica 1320 Chile O. ficus-indica 1376 Mexico AN-V1 Opuntia spp. 1393 Mexico

Weight per seed (mg)

Seed weight per fruit†‡ (g)

Species Acc. #, Origin and UAAAN code*

5·7±0·4

5·6±0·4

6·0±0·2

5·7±0·2

5·7±0·2

5·8±0·4

5·6±0·2

5·9±0·2

5·7±0·2

5·7±0·2

Fruit width† (cm)

Table 3. (continued)

7·3±0·4

7·3±0·4

9·3±0·2

9·2±0·6

8·8±0·6

10·1±0·6

8·9±0·4

7·7±0·4

8·1±0·4

7·5±0·4

Fruit length† (cm)

27·3±1·8

25·8±2·0

24·5±1·1

28·5±1·3

21·9±1·3

25·2±3·0

28·1±1·1

25·7±1·3

23·5±1·5

25·4±1·8

Scar diam.† (mm)

2·7±0·9

2·5±1·1

6·6±0·9

0·8±0·6

5·6±1·1

6·9±1·1

2·1±0·6

3·4±0·7

6·1±0·9

3·0±1·3

Scar depth† (mm)

OPUNTIA FRUIT FROST HARDINESS 133

O. inermis 1270 Brazil O. ficus-indica 1277 Mexico O. ficus-indica 1278 Mexico O. ficus-indica 1279 Mexico O. streptacantha 1281 Mexico O. ficus-indica 1282 Mexico O. hyptiacantha 1287 Mexico O. ficus-indica 1294 Mexico O. megacantha 1297 Mexico O. ficus-indica 1300 Mexico O. ficus-indica 1301 Mexico O. ficus-indica 1319 Chile O. ficus-indica 1320 Chile

Species Acc. #, Origin and UAAAN code*

0·068 0·051

12

14

12

14

14

13

0·056

0·090

0·021

0·005

0·043

0·006

12

13

0·001

Fruit width (L)

0·098

0·096

Fruit length (Q)

14

Fruit length (L)

0·060

0·013

Scar diam. (Q)

13

0·090

Scar diam. (L)

0·045

0·040

Scar depth (Q)

18

16

13

N

Scar depth (L)

Table 4. p-values for significant (p<0·10) linear (L) and quadratic (Q) regression relationships between sugar content and fruit length, fruit width, scar diameter and scar depth for cactus pears harvested in the summer of 1995 in Kingsville, Texas

0·047

Fruit width (Q)

134 J. PARISH & P. FELKER

Fruit length (L)

0·094

Fruit length (Q)

Fruit width (L)

15

0·097

0·003

Scar diam. (Q)

12

0·013

Scar diam. (L)

0·073

Scar depth (Q)

13

14

14

14

12

13

13

N

Scar depth (L)

*Designation of clone by Universidad Autonoma Agraria Antonio Narro.

O. ficus-indica 1321 Chile O. ficus-indica 1376 Mexico AN-V1 O. crassa 1379 Mexico AN-V4 O. megacantha 1380 Mexico AN-V5 O. megacantha 1383 Mexico AN-T3 O. megacantha 1390 Mexico AN-TV6 Opuntia sp. 1392 Mexico Opuntia sp. 1393 Mexico Opuntia sp. 1398 Mexico

Species Acc. #, Origin and UAAAN code*

Table 4. (continued)

Fruit width (Q)

OPUNTIA FRUIT FROST HARDINESS 135

136

J. PARISH & P. FELKER

significant (p < 0·10) quadratic coefficients for sugar content and fruit scar diameter, Mexican accessions 1287 (p = 0·005) and 1380 (p = 0·003) had the lowest p-values. Chilean accession 1319 had the most number of significant (p < 0·10) relationships (4) between morphological features and sugar content.

Relationships between fruit weight, peel weight, pH and fruit sugar Relationships between fruit pH and sugar content were the most frequent compared to all the variables tested in the trial and were significant (p < 0·10) for nine of the 22 accessions (1270, 1278, 1279, 1294, 1300, 1376, 1383, 1392 and 1398) and thus may be the most useful characteristic in predicting fruit maturity as judged by sugar content (Table 5). Only one accession (1383) had a significant (p = 0·042) quadratic coefficient for fruit pH and sugar content with no significant (p = 0·153) linear regression relationship. Pulp weight and sugar content had a significant (p < 0·10) linear regression relationships with seven accessions (1277, 1278, 1281, 1282, 1301, 1321, and 1393). Only Mexican accessions 1278 and 1279, both from Chapingo, had some significant (p < 0·10) linear regression relationship or quadratic coefficient for all four variables (fresh weight, pulp weight, peel weight and pH). Fresh weight, pulp weight and pH had more significant (p < 0·10) linear regression relationships with fruit sugar content than significant (p < 0·10) quadratic coefficients. Brazilian accession 1270 had the strongest (p = 0·0001) linear regression relationship between pH and sugar content. Accession 1383 (AN-T3) was the only variety to have a significant (p = 0·042) quadratic coefficient between sugar content and pH. Accession 1379 (AN-V4) was the only accession not to have a significant (p < 0·10) relationship with any of the measured variables in our trial. Accession 1287 (p = 0·042) and 1297 (p = 0·027) had significant (p < 0·10) linear regression relationships between sugar content and picked fruit height. Accession 1390 (AN-TV6) was the only variety to have a significant (p = 0·013) quadratic coefficient for sugar content and picked fruit height.

Discussion The two fruit clones with the highest mean sugar content (13·8 and 14·6%) were both of Chilean origin. All Chilean fruit clones (3) in this trial also had a higher mean sugar content than the previously reported 12% sugar for a Chilean fruit clone grown in a Texas greenhouse (Russell & Felker, 1987). While only a few fruits of top ranking variety 1321 were measured in a previous trial at 13·7% sugar (Gregory et al., 1993), we found the fruits of accession 1321 to be very similar at 13·8% sugar. Thus, with the exception of the Chilean varieties and Mexican clones 1383 and 1294, our values were similar to that reported by Gregory et al. (1993), where sugar for Opuntia fruit averaged between 11 and 14%. Likewise, sugar measurements in our trial were also comparable to reports in Israel where the sugar content averaged 11·8% in winter and 12·8% in the summer (Nerd et al., 1991). Some sugar contents were lower than reported values from Mexico where sugar contents for 18 selected varieties averaged between 12 and 17% (Pimienta, 1994). Mondragon & Perez (1994) reported that the leading cactus pear cultivar in Central Mexico (Reyna) had 14·8% sugar. While this sugar content is comparable to Chilean accession 1319, Reyna had greater seed content and greater yield potential. Though we experienced great variability in fruit yields between blocks, the magnitude of our fruit production was similar to reports in Italy at 13–33 ton ha–1 (1·3–3·3 kg m–2) (Inglese et al., 1995a,b). The Mexican varieties whose estimated yields averaged between 0·2 and 5·2 kg m–2 (2 to 52 ton ha–1) had the greatest range

OPUNTIA FRUIT FROST HARDINESS

137

in productivity. However, as mentioned in the materials and methods, our yields are an overestimate of what would be obtained in commercial production as they were based on unbuffered row-plots of five plants. Pimienta (1994) reported fruit production for typical plantations in Mexico to be a very low 2–8 tons ha–1, due to insufficient fertilization, pruning, and weed control. California fruit yields reported by D’Arrigo Bros., which ranged between 7 and 14 tons ha–1, were similar to nine of the 22 accessions in our trial and slightly higher than in Mexico (Curtis, 1977). Since seediness is a major obstacle to commercialization in cactus pear (Caplan, 1995), low seed weights and low seed number are crucial for its success in the world market. Seed weight per fruit in our trial, which averaged between 2 and 6 g, was slightly lower than previously reported Mexican values averaging between 3 and 8 g (Pimienta, 1994). Twenty of the 22 accessions in our trial had mean seed weights lower than that for the most widely used cultivar in Central Mexico, which was 5·2 g fruit–1 (Mondragon & Perez, 1994). The lowest mean seed weight per fruit values observed in this trial compare very favorably to the ‘parthenocarpic’ BS1 clone reported by Weiss et al. (1993). The mean seed weight per fruit we measured for Chilean clones (2·2 g fruit–1 for 1319 and 2·3 g fruit–1 for 1321) and for Mexican clones (2·2 g fruit–1 for 1282 and 2·3 g fruit–1 for 1279) compare favorably to BS1 seed weights of 2·0 g fruit–1 measured in the autumn. In the spring the BS1 clone had lower seed weights (0·9 g fruit–1) but had smaller mean fruit weights (100 g) as well. The peel to pulp ratio of clone BS1 of 2·4 in the spring was much greater (less desirable) than values of 1·6 for clone 1319 and 1·3 for clone 1321. Thus, when combined with outstanding sugar contents and low seed weight per fruit values, the Chilean clones appear exceptional. There have been many conflicting reports on the existence of vegetative parthenocarpy in cactus pear. Gil et al. (1977) reported that fertilization is needed for fruit set while Pimienta (1990) suggested that vegetative parthenocarpy cannot exist in cactus pear because the pulp develops from the seed. Nonetheless, research in Chile has revealed that gibberellic acid sprayed on intact and emasculated flowers yielded parthenocarpic fruits of normal size containing false seeds consisting only of ovule integuments (Diaz & Gil, 1978; Gil & Espinoza, 1980). Since fruits would need to be treated individually, the induction of parthenocarpy in this manner may not be a viable alternative for commercial production. Studies in Israel have revealed a suspected parthenocarpic clone (BS1) that produced 100% aborted seeds without growth hormones (Weiss et al., 1993). In BS1, flowers are produced with incomplete pollen tubes penetrating only to the micropyle, and thereby need no fertilization for fruit set and development. Ovules of BS1 were notably larger than other seeded clones, suggesting that a thicker nucellus may be the physical barrier that prevents the male gametes from fertilizing the embryo within the ovules. This would be consistent with Tisserat et al. (1979) who stated that there are many wild and ornamental varieties of Opuntia that set fruit without pollination by means of nucellar embryogenesis. In this state, a degenerating embryo is replaced by an enlarged nucellus that divides to form a proembryo. An enlarged nucellus is apparently not the only barrier to successful sexual reproduction in Opuntia. Its ovules possess a circinotropic shape, with an extended funicular stalk causing the ovule to wrap around on itself (Fahn, 1967), covering the entrance to the embryo through the micropyle. Also, different levels of ploidy (2 3 , 3 3 , 4 3 , 5 3 , 6 3 , 8 3 , 10 3 , 11 3 , 12 3 , 13 3 , 19 3 and 20 3 ) in cactus pears (Pimienta & Munoz, 1995) may result in aneuploidy, an uneven matching of chromosomes during metaphase, which may in turn cause seeds to abort (Srb et al., 1965). Perhaps the low mean number of seeds for Mexican accession 1279 (144) and Chilean variety 1321 (174) may be a result of aborted seeds from aneuploidy. In Mexico during the 1500s, the native American Indians were known to trek hundreds of miles to reach isolated clusters of particularly sweet cactus pears (Ciesla,

O. inermis 1270 Brazil O. ficus-indica 1277 Mexico O. ficus-indica 1278 Mexico O. ficus-indica 1279 Mexico O. streptacantha 1281 Mexico O. ficus-indica 1282 Mexico O. hyptiacantha 1287 Mexico O. ficus-indica 1294 Mexico O. megacantha 1297 Mexico O. ficus-indica 1300 Mexico O. ficus-indica 1301 Mexico O. ficus-indica 1319 Chile O. ficus-indica 1320 Chile

Species Acc. #, Origin and UAAAN code*

0·012

18

14

12

12

14

14

13

0·096

0·013

12

13

0·092

14

13

0·062

16

13

N

Fresh wt. (L)

0·001

Fresh wt. (Q)

0·066

0·020

0·005

0·008

0·016

Pulp wt. (L)

0·045

0·029

0·065

Pulp wt. (Q)

0·035

0·034

Peel wt. (L)

0·027

0·033

0·001

0·042

Peel wt. (Q)

0·016

0·012

0·019

0·006

0·001

pH (L)

Table 5. p-values for significant (p<0·10) linear (L) and quadratic (Q) regression relationships between sugar content and fresh weight, pulp weight, peel weight and fruit pH for cactus pears harvested in the summer of 1995 in Kingsville, Texas

pH (Q)

138 J. PARISH & P. FELKER

15

12

13

14

14

14

12

13

13

N

0·094

0·052

Fresh wt. (L)

Fresh wt. (Q)

0·031

0·018

Pulp wt. (L)

*Designation of clone by Universidad Autonoma Agraria Antonio Narro.

O. ficus-indica 1321 Chile O. ficus-indica 1376 Mexico AN-V1 O. crassa 1379 Mexico AN-V4 O. megacantha 1380 Mexico AN-V5 O. megacantha 1383 Mexico AN-T3 O. megacantha 1390 Mexico AN-TV6 Opuntia sp. 1392 Mexico Opuntia sp. 1393 Mexico Opuntia sp. 1398 Mexico

Species Acc. #, Origin and UAAAN code* Pulp wt. (Q)

Table 5. (continued)

Peel wt. (L)

0·037

Peel wt. (Q)

0·055

0·052

0·030

pH (L)

0·042

pH (Q)

OPUNTIA FRUIT FROST HARDINESS 139

140

J. PARISH & P. FELKER

1988). Some of these clusters, known as ‘backyard’ varieties, are of higher quality than wild strains (Pimienta, 1994). This would suggest that cross pollination and fertilization in the wild was still taking place as recent as the age of man. Perhaps the expansion of drier areas into some previously more mesic environments (Axelrod, 1958) eliminated a key pollinator that was once instrumental in sexual reproduction in Opuntia. Such an event would not be wholly disastrous for Opuntia since fragmentation allows it to vegetatively reproduce. Perhaps the success of asexually reproducing (Mondragon & Pimienta, 1995) has eliminated the evolutionary pressure to maintain the necessary forms and functions required for sexual reproduction. Since Opuntia does produce flowers and has great genetic diversity in Mexico (Pimienta, 1994), it is possible that at some time in the relatively recent past this genus relied more heavily on sexual reproduction as a means of propagation. Using Italian standards, where cactus pears have been cultivated for nearly half a millennia, first class fresh fruit weighs between 120 and 160 g. Based on this grading, 17 of the 22 accessions in our trial produced first class fruits while only five accessions produced second class fruits (Inglese et al., 1995b). Fruit weight in our trial could have been increased by thinning the number of fruits per cladode to less than six as suggested by Inglese et al. (1995a). Mean fresh weights for five accessions in our trial were similar or higher than that for Reyna, the leading cactus pear cultivar in central Mexico, at 141 g (Mondragon & Perez, 1994). The largest fruits (160 g) in our study were produced by spiny orange–yellow accession 1287. In Mexico however, varieties such as Cristalina and Burrona weigh 240 and 205 g, respectively (Pimienta, 1994). In this summer fruit trial, 15 of the 18 Mexican accessions and all of the Chilean and Brazilian accessions produced fruits with a higher mean fresh weight than Israel’s summer fruit crop (116 g). Yet all the accessions in our trial produced less than Israel’s winter crop (178 g) (Nerd et al., 1991). The mean pulp weights in our study averaged between 47 and 81 g and were generally lower than the reported values for Mexican varieties (Pimienta, 1994). Pulp weights in our trial (59–152 g) were similar to reported values from Israel where summer pulp weight was 62 g (Nerd et al., 1991). Peel weights averaged between 41 and 87 g and were similar to fruits produced in Mexico where peel weights averaged from 52 to 79 g (Pimienta, 1994) and in Israel where summer crop peel weight was 57 g (Nerd et al., 1991). The mean pH values ranged from 5·6 to 6·5 and were generally lower than reported in Mexico where 18 selected fruits ranged from 6·4 to 7·1. When compared with reports from Gregory et al. (1993) where pH ranged from 4·1 to 6·1, our trial overall yielded fruits that were less acidic. Gregory et al. (1993) also noticed that varieties with lower pH (less than 5) generally had lower sugar contents and cited a significant (p < 0·10) relationship between sugar content and pH in Opuntia fruit (p = 0·002). The significant (p < 0·10) relationship between sugar content and pH as observed by Gregory et al. (1993) is probably related to maturity, i.e. as the fruit becomes more mature, the pH increases with sugar content. This is supported by nine accessions in our trial that showed significant (p < 0·10) linear regression relationships between sugar content and pH. However, there were two accessions (1383 and 1320) that had a lower pH value of 5·9 with higher sugar contents. One of us (J.P.) feels that 1383 has a more pleasing taste than the other varieties due to a high sugar content/lower pH combination.

Summary While Chilean clones had the highest fruit sugar, Mexican clones were the highest producers of fruit. Perhaps cultural practices can be identified that will permit either Chilean varieties to have higher yields or Mexican varieties to have greater sugar content. In Israel applications of N fertilizer (0, 30, 60, 120 kg ha–1 at the end of the

OPUNTIA FRUIT FROST HARDINESS

141

summer has increased bud initiation in the autumn and the number of buds in the following spring (Nerd et al., 1993). Studies by Karim et al. (1996) have found positive correlations between cladode Mg concentration and fruit sugar content. While some researchers have suggested that fruit maturity in Opuntia might be determined through morphological characters, this trial has shown a great variability between accessions in morphologic/maturity relationships as determined through sugar content. Morphological characters such as scar depth may not be as helpful as scar diameter in determining fruit maturity in cactus pear. Since economic returns for cattle-based forage systems in semi-arid regions only range from $2–3 ha–1 year–1 (Gregory et al., 1993), developing high value drought resistant crops for these areas is essential. Since a single clone that possesses all the desirable traits has not yet been identified, selecting the most desirable traits in various clones for use in a breeding program is necessary. Unfortunately little is known about breeding techniques, such as emasculation and seed germination in Opuntia. Of the six UAAAN varieties developed by Borrego-Escalente et al. (1990) that produced fruit in this trial, accession 1380 (AN-V5) is most promising as it had the greatest yields, but unfortunately had an unacceptable sugar content of only 11·1%. Accession 1383 (AN-T3), with a much lower estimated yield, had an acceptable sugar content (13·4%) and lower pH (5·9), resulting in a good acidity/sugar taste combination. In spite of the thorns on this variety, accession 1383 (AN-T3) possessed a good balance of agronomic and fruit quality characteristics. While accessions 1279, 1281, 1282, and 1300 from the research station at Chapingo, Mexico are all thornless, produce red or purple fruit, and rank high in either yield, pulp weight, fruit length, fruit width, low seed weight, and low seed number, they unfortunately had low frost scores. For example, in the mild freeze of 1991 (–7°C) many accessions from this region had 50% of their above-ground height killed (Gregory et al., 1993). Thornless accession 1277 deserves further attention as it was the only accession from central Mexico (Milpa Alta) that had both high yield and high frost resistance. While Mexico contains the greatest source of genetic diversity in Opuntia, the Chilean clones possessed exceptional fruit characteristics, i.e. sugar content, and low seed weight that rivaled the Mexican varieties. Chilean clone 1321 also had the greatest cold resistance of the varieties examined thus far. These Chilean clones also compared favorably in seed weight per fruit and peel/pulp ratio with parthenocarpic clones (BS1) grown in Israel. While no single Chilean clone has high sugar, low seed number, high freeze hardiness and high productivity, these varieties still represent good genetic stock for further hybridization and research. However, in the south Texas environment, Mexican clones still dominate in fruit production. The financial assistance of the International Arid Lands Consortium Cooperative Agreement 28-G3-694 and the USDA CSRS Agreement No. 95 34312-1309 is gratefully acknowledged. Publication number 97–117 of the Caesar Kleberg Wildlife Research Institute.

References Axelrod, D.I. (1958). Evolution of madro-tertiary geoflora. The Botanical Review, 24: 422–509. Barrientos, P.F., Borrego-Escalente, F. & Felker, P. (1992). Collaborative Mexico/United States initiative to breed freeze tolerant fruit and forage Opuntia varieties. In: Felker, P. (Ed.), Third Annual Prickly Pear Council, 49–55. Kingsville: TX Texas A&M Univ. 65 pp. Benson, L. (1982). Cacti of the United States and North America. Stanford, CA: Stanford University Press. 1044 pp.

142

J. PARISH & P. FELKER

Borrego-Escalente, F., Murillo-Soto, M. & Parga-Torres, V.M. (1990). Potencial de produccion en el norte de Mexico de variedades de nopal (Opuntia spp.) tolerantes al frio. In: Felker, P. (Ed.), Proceedings of the First Annual Texas Prickly Pear Council, pp. 49–73. Kingsville: Caesar Kleberg Wildlife Research Institute. 95 pp. Cantwell, M. (1991). Quality and postharvest physiology of ‘nopalitos’ and ‘tunas’. In: Felker, P. (Ed.), Second Annual Texas Prickly Pear Council, pp. 50–66. Kingsville: Caesar Kleberg Wildlife Research Institute. 123 pp. Caplan, K. (1995). Merchandising, distribution and marketing nopalitos and cactus pears. In: Felker, P. & Moss, J. (Eds), Proceedings Professional Associates for Cactus Development. First Annual Conference, pp.47–48. Dallas, TX: Prof. Assoc. Cactus Devel. 92 pp. Ciesla, B. (1988). Opuntia: Points about Prickly Pear. Americas, 40: 10–15. Curtis, J. (1977). Prickly pear farming in the Santa Clara Valley, California. Economic Botany, 31: 175–179. Diaz, F. & Gil, G. (1978). Effectividad de diversas dosis y metodos de aplicacion del acido giberelico en la induccion de partenocarpia y en el crecimiento del fruto de tuna (Opuntia ficus-indica, Mill.). Ciencia e Investigacion Agraria, 5: 106–117. Fahn, A. (1967). Plant Anatomy. Oxford: Pergamon Press. 534 pp. Gil, G. & Espinoza, A.R. (1980). Desarrollo de frutos de tuna (Opuntia ficus-indica, Mill.) Con aplicacion prefloral de giberelina y auxina. Ciencia e Investigacion Agraria, 7: 141–147. Gill, G., Morales, M. & Momberg, A. (1977). Cuaja y desarrollo del fruto de tuna (Opuntia ficus-indica, Mill.) y su relacion con polinizacion y con los acidos giberelico y cloroetilfosfonico. Ciencia e Investigacion Agraria, 4: 163–169. Gregory, R., Kuti, J. & Felker, P. (1993). A comparison of Opuntia fruit quality and winter hardiness for use in South Texas. Journal of Arid Environments, 24: 37–46. Griffiths, D. (1905). The prickly pear plant and other cacti as food for stock. (I). USDA Plant Industry Bulletin No. 74. 47 pp. Griffiths, D. (1915). Hardier spineless cactus. Journal of Heredity, 6: 182–191. Griffiths, D. & Hare, R.F. (1907). The tuna as a food for man. U.S.D.A. Bulletin 116. Washington, D.C.: G.P.O. 66 pp. Inglese, P., Barbera, G., La Mantia, T. & Portolano, S. (1995a). Crop production, growth, and ultimate size of cactus pear fruit following fruit thinning. HortScience, 30: 227–230. Inglese, P., Barbera, G. & La Mantia, T. (1995b). Research strategies in the development of cactus pear (Opuntia spp.) for fruit production. Journal of Arid Environments, 29: 455–468. Karim, M.R., Felker, P. & Bingham, R.L. (1996). Correlations between cactus pear (Opuntia spp.) cladode nutrient concentrations and fruit yield and quality. Journal of Plant Nutrition (in review). Kingsville Record and Bishop News. (1996). 1996 Annual rainfall total, Vol 90: 55, p. 4A. Kingsville TX, January 7, 1996. Kluge, M. & Ting, I.P. (1978). Crassulacean Acid Metabolism: Analysis of an ecological adaptation. Berlin: Springer-Verlag. 209 pp. Martinez, L.M. (1968). Estudios del nopal rastrero forrajero y del nopal frutal. In: Box, T.W. & Rojas-Mendoza, P. (Eds), Proceedings of International Symposium on Increasing Food Production in Arid Lands. Lubbock, TX: ISCALS pub. 3:39–344. Mondragon, J.C. & Perez, G.S. (1994). ‘Reyna’ (syn. ‘Alfajayucan’) is the leading cactus pear cultivar in Central Mexico. Fruit Varieties Journal, 48: 134–136. Mondragon, J.C. & Pimienta, B.E. (1995). Propagation. In: Barbera, G., Inglese, P. & Pimienta-Barrios, E. (Eds), Agro-ecology, Cultivation and Uses of Cactus Pear. FAO Plant Production and Protection Paper 132. Rome: FAO. 216 pp. Nerd, A., Karady, A. & Mizrahi, Y. (1991). Out of season prickly pear: fruit characteristics and effect of fertilization and short droughts on productivity. HortScience, 26: 337–342. Nerd, A., Mesika, R. & Mizrahi, Y. (1993). Effect of N fertilizer of autumn flush and cladode N in prickly pear (Opuntia ficus-indica (L.) Mill.). Journal of Arid Environments, 68: 337–342. NOAA (1992). Climatography of the United States No. 81. Texas, monthly station normals of temperature, precipitation and cooling degree days, 1961–1990. Washington, D.C.: U.S. Department of Commerce Publisher. Pimienta, E. (1990). El Nopal Tunero. Guadalajara, Mexico: University Guadalajara Publisher. 246 pp. Pimienta, B.E. (1994). Prickly pear (Opuntia spp.) A valuable fruit crop for the semi-arid lands of Mexico. Journal of Arid Environments, 28: 1–11.

OPUNTIA FRUIT FROST HARDINESS

143

Pimienta, B.E. & Engleman, M. (1985). Desarollo de la pulpa y proporcion en volumen, de los componentes del loculo maduro en tuna (Opuntia ficus-indica (L.) Mill.). Agrociencia, 62: 51–56. Pimienta, B.E. & Munoz, U.A. (1995). Domestication of Opuntias and cultivated varieties. In: Barbera, G., Inglese, P. & Pimienta-Barrios, E. (Eds), Agro-ecology, Cultivation and Uses of Cactus Pear. FAO Plant Production and Protection Paper 132. Rome: FAO. 216 pp. Russell, C.E. & Felker, P. (1987). The prickly pears (Opuntia spp., Cactaceae): a source of human and animal food in semi-arid regions. Economic Botany, 41: 433–445. Srb, A.M., Owen, R.D. & Edgar, R.S. (1965). General Genetics. San Francisco, CA: W.H. Freeman & Company. 577 pp. Tisserat, B., Esan, B.E. & Murashige, T. (1979). Somatic embryogenesis in angiosperms. Horticultural Reviews, 1: 1–78. Uphof, J.C. Th. (1916). Cold resistance in spineless cacti. University of Arizona Agricultural Experiment Station Bulletin no. 79: 119–144. USDA (1975). Soil Taxonomy. U.S.D.A. Agric. Handbook, No. 436. Washington D.C. 754 pp. USDA (1978). Hidalgo series. National Cooperative Soil Survey. Washington D.C.: U.S. Govt. Printing Office. 171 pp. Weiss, J., Nerd, A. & Mizrahi, Y. (1993). Vegetative parthenocarpy in the cactus pear (Opuntia ficus-indica (L.) Mill. Annals of Botany, 72: 521–526.