- Email: [email protected]
Maturation of sunflower and sector sampling of heads to monitor maturation
Field Crops Research, 7 (1983) 31--39
31
Elsevier Science Publishers B.V., Amsterdam - - Printed in The Netherlands
MATURATION OF SUNFLOWER AND SECTOR SAMPLING OF HEADS TO MONITOR MATURATION
R O B E R T G. R O B I N S O N
Department of Agronomy and Plant Genetics, University of Minnesota, St. Paul, MN 55108 (U.S.A.) Minnesota Agricultural Experiment Station Scientific Journal Series paper 11,400. (Accepted 5 January 1983)
ABSTRACT Robinson, R.G., 1983. Maturation of sunflower and sector sampling of heads to monitor maturation. Field Crops Res., 7: 31--39. Research was undertaken to relate visual appearance of sunflower (Helianthus annuus L.) plants with achene maturation and to determine if severing stalks before physiological maturity stops achene growth. A new technique for studying maturation involved harvesting sectors of achenes at different times from the same head receptacle and determining weight per 100 achenes. Economic physiological maturity occurs at the stage when achenes reach maximum weight. These individual head studies with diverse cultivars and plant populations showed that maturity occurred after backs of heads were completely yellow. Leaf loss was not a reliable indicator of physiological maturity. Each year, about 1350 growing degree-days (GDD) occurred between planting and physiological maturity. The interval between physiological maturity and brown senescence of heads averaged 10, 13, 14, and 18 days for 4 years. Whole plot studies showed that the accuracy of maturation ratings based on average heads may be affected by later-than-average heads. Sunflower heads were about 80% water at the initiation of yellowing and 19 to 45% water at brown senescence. Achene size was determined before head yellowing whereas yield, oil percentage, weight/hi, and weight per-achene increased during the maturation period. Achenes from severed plants dried in the field and from heads harvested the same day but dried in an oven did not differ in yield or other characteristics indicating that achene development stops when stalks are cut.
INTRODUCTION
Five growth periods of six sunflower (Helianthus annuus L.) Cultivars averaged 11 days from planting to emergence, 33 days from emergence to head visible, 27 days from head visible to first anthesis, 8 days from first to last anthesis, and 30 days to physiological maturity over a 3-year period (Robinson, 1971). All stages can be identified precisely except physiological maturity. Consequently, maturity is estimated visually by the change from green to yellow coloration of the backs of the heads and involucral bracts. Backs of the heads and stalks become brown as senescence proceeds. 0378-4290/83/$03.00
© 1983 Elsevier Science Publishers B.V.
32 Anderson (1975) defined physiological maturity as the time when achene dry weight, oil percentage, and linoleic acid percentage reach their maximum. At that time, the backs of heads were yellow b u t 10% were brown, and the achenes were 40% water. Robertson et al. (1978) harvested heads at weekly intervals from 7 to 70 days after first anthesis. Maximum achene weight and oil percentage occurred 35 days after first anthesis when achenes were 36% water. This research embraced one cultivar for 1 year, and the authors sampled only the achenes from the outer 3 to 7 cm of the heads. Browne (1978) sampled 10 achenes, from the radial arcs of VNIIMK 6540 cultivar at various dates and found that the achenes reached maximum dry weight 31 days after last anthesis when achene moisture was 29%. This stage occurred in the middle of the 3.5 day interval between the first and last abscission of the diskflorets (corollas and enclosed stigma, style, and stamen remnants). The objectives of this research were to: ascertain lengths of some maturation periods between the initiation of head yellowing and brown senescence; determine if head yellowing is a reliable indicator of physiological maturity; and find o u t if severing the stalks before physiological maturity stops achene growth. MATERIALS AND METHODS Trials were c o n d u c t e d on Typic Hapludoll~ fine silty over sandy or sandyskeletal, mixed, mesic (Waukegan silt loam) soil at Rosemount, MN. R o w spacings were 102 cm in 1970 and 1971 and 76 cm in 1972 and 1980. Separate trials involved individual plants and bulked plants from whole plots. Individual head studies Arrowhead and Mingren nonoilseed cultivars and Peredovik and P-21ms X HA 60 oilseed cultivars were planted 3 May 1970, 2 May 1971, and 4 May 1972. Nonoilseed cultivar USDA 924 and oilseed cultivars USDA 894 and USDA 903 were planted 5 May 1980. Arrowhead, Mingren, and Peredovik are n o t hybrids; the other cultivars are single-cross hybrids. Plant populations for all cultivars were 57,000 plants per ha in 1970 through 1972 and 49,000 and 25,000 plants per ha in 1980. Achenes from the same head were harvested at three stages of maturation from receptacle sectors of 12 to 15 heads of each cultivar at each population (Fig. 1). All achenes in a sector were taken except those along the exposed edge of the previous sector. Heads with sectors of achenes removed continued to mature like nearby unsampled heads. Maturation stages included: premature -- backs of heads and involucral bracts greenish yellow to yellow; early maturity -- backs of heads and involucral bracts 90 to 100% yellow; and early senescence -- backs of heads and involucral bracts 95 to 100% brown. Each sample of achenes was placed in a separate plastic bag and later,
33
Fig. 1. Immature sunflower head with disk flower corollas removed from one sector (A) exposing the achenes and the achenes removed from another sector (B) exposing the receptacle.
the same day, passed through a fanning mill to remove sterile achenes. Fertile achenes were weighed, dried at 70°C for 4 days, and then dried at 100°C for 4 h and weighed again to allow calculation of achene moisture percentage. Variables measured for each sector on each head included achene moisture and oil percentages, weight per 100 achenes, and growing degree-day (GDD) summations between date of planting or first anthesis to date of harvest. Oil percentages were determined at the University of Illinois with nuclear magnetic resonance equipment. Daffy maximum and minimum temperatures were taken from an official weather station a b o u t 1 km away. GDD for each d a y in centrigrade units were calculated by averaging the minimum and m a x i m u m temperatures and subtracting 7.2°C base temperature (Robinson et al., 1967). Trials for each o f first 3 years were analyzed as randomized blocks using heads, cultivars, sectors (maturation stages), and cultivars X sectors as components of variation and interactions with heads as error. The 1980 trial was analyzed as a split split-plot with heads, cultivars, populations, cultivars × populations, sectors, cultivars × sectors, populations X sectors, and cultivars × populations × sectors as components of variation and appropriate interactions with heads as error.
34 TABLE I Average o f f o u r s u n f l o w e r cultivars in 1 9 7 0 , 1 9 7 1 , a n d 1 9 7 2 a n d o f t h r e e cultivars in 1 9 8 0 f o r weight, oil p e r c e n t a g e , a n d m o i s t u r e p e r c e n t a g e o f a c h e n e s r e m o v e d f r o m t h e h e a d s a t t h r e e stages o f m a t u r a t i o n a a n d d a y a n d g r o w i n g degree-day ( G D D ) s u m m a t i o n at t h e s e stages 1970
1971
1972
1980
A c h e n e w e i g h t / 1 0 0 (g) Premature Early maturity Early senescence LSD ( 0 . 0 5 )
7.2 7.3 7.5 0.3
7.9 9.0 9.1 0.2**
6.5 7.0 7.3 0.4**
32.4 32.6 32.5 1.1
31.9 34.2 34.7 2.0**
33.5 34.7 34.6 1.3
39.6 33.6 11.9 5.1"*
54.0 41.3 14.1 2.4**
54.8 44.4 18.2 2.4**
-7.2 7.1 0.1"*
A c h e n e oil (%) Premature Early maturity Early senescence LSD (0.05)
-----
A c h e n e w a t e r (%) Premature Early maturity Early senescence LSD ( 0 . 0 5 )
-36.6 16.0 1.2"*
Planting to achene removal (days) Premature Early maturity Early senescence
106 111 121
107 113 131
106 112 126
-114 127
1342 1409 1549
1169 1253 1484
1209 1293 1452
-1445 1620
31 38 56
30 36 50
-43 56
373 456 688
392 477 635
-617 785
Planting to achene removal (GDD) Premature Early maturity Early senescence F i r s t a n t h e s i s t o a c h e n e r e m o v a l (days) Premature Early maturity Early senescence
--
---
First anthesis to achene removal (GDD) Premature Early maturity Early senescence
--
---
a p r e m a t u r e - - b a c k s o f h e a d s greenish y e l l o w t o yellow. E a r l y m a t u r i t y - - b a c k s o f h e a d s 9 0 t o 1 0 0 % yellow. E a r l y s e n e s c e n c e - - b a c k s o f h e a d s 9 5 t o 100% b r o w n . * * F s i g n i f i c a n t at 0 . 0 1 level.
35
Whole plot studies Arrowhead and Mingren nonoilseed cultivars plus Peredovik and P-21ms × HA 60 oilseed cultivars were planted 3 May 1970 and 1 May 1971. Oilseed hybrid cultivars P-21ms × HA 60 and cmsHA 93 X R H A 265 were planted 4 May 1972. Whole heads were harvested at five stages of maturation in 1970 and six stages o f maturation in 1971 and 1972. Maturation stages ranged from disk corollas remaining and head yellowing to brown senescence (Table II). Split-plot experimental designs involved cultivars replicated three times as main plots and maturation stages as subplots. Subplots were three rows 6 m long. A 5-m length of the center row was harvested to measure head moisture percentage and achene yield per ha. Heads were severed close to the receptacle, weighed, dried at 70°C for 3 weeks, weighed again, and head moisture percentage calculated. Heads were threshed and achene yield, test weight, weight/100, oil percentage, and large size percentage determined. Large achene percentage was measured b y sieving 100-g samples. Achenes held on 0.79, 0.64, 0.56, 0.56, and 0.48 cm round-hole screens were considered large for Mingren, Arrowhead, Peredovik, P-21ms × HA 60, and cmsHA 93 × R H A 265, respectively. Additional subplots were included for all treatments in 1970 and for the first t w o maturation stages in 1971. On these subplots, stalks were cut 20 cm above the soil to simulate a windrower or corn binder. A 5-m length of each center row was left to dry in a windrow. After drying to less than 15% achene moisture, heads were severed from the stalks, dried at 70 ° C, and processed like the other treatments. RESULTS AND DISCUSSION
Individual head studies Achene yield o f a sunflower head is the product of the number of fertile achenes and the weight per fertile achene. Since the number of fertile achenes is determined prior to maturation, m a x i m u m yield occurs when the fertile achenes reach their m a x i m u m weight. Significant increases in achene weights and achene oil percentages did n o t occur after 111 days from planting in 1970, 113 days in 1971, 112 days in 1972, and 114 days in 1980 (Table I). Consequently, achenes at these dates were near physiological maturity, and achene moisture percentages averaged from 34 to 44% among years. Backs o f the heads and involucral bracts were 90 to 100% yellow at this stage. Cultivars differed in maturity, head type, achene size, achene oil percentage, disease resistance, leaf retention, and disk corolla retention. Despite these differences, mean squares for the interactions of maturation stages X cultivars and maturation stages × populations were either nonsignificant or
36 significantly less than the mean squares for maturation stages. Consequently average data are shown in Table I. Day and GDD summations are two c o m m o n methods of designating maturity of corn {Zea mays L.) and pea (Pisum sativum L.). GDD summations are usually less variable among years than are day summations, so they are used by the canning industry to predict harvest time for individual fields. Robinson et al. (1967) used four different base temperatures for GDD summations between planting and anthesis for eight sunflower cultivars at nine locations ranging from 31 to 49 degrees latitude in North America. They concluded that any reasonable base temperature was satisfactory for comparisons within a narrow range of latitudes. The 7.2°C base temperature used in this research lies between the 10°C base for corn and the 4.4°C base for pea. Day and GDD summations from planting and from first anthesis to early maturity and to early senescence were useful b u t n o t precise predictors of maturation stages. Data in Table I do n o t support using date of first anthesis rather than date of planting to begin day or GDD summations to maturity. In 1980, 87% o f the upper leaves were still green at early maturity and then declined to only 4% green leaves at early senescence. Leaf retention was much less in the first 3 years with nonhybrid cultivars. Hybrid cultivars and populations also differed significantly in leaf retention. Green leaf retention at early maturity was 22% greater for the 25,000 plant/ha population. Consequently, leaf loss was n o t a reliable indicator of physiological maturity. Preharvest desiccants are used to kill sunflower and advance senescence to the b r o w n stage more rapidly than it occurs naturally. The time between the start of physiological maturity and brown senescence was 10 days in 1970, 18 in 1971, 14 in 1972, and 13 in 1980 (Table I). Sunflower plants do n o t become completely brown for at least 2 days after spraying, and it is illegal to harvest within 7 days of spraying. Consequently, the potential advance in senescence from spraying the average head was n o t great. However, desiccants may advance harvest date considerably in fields with heads in various stages of maturation or with cultivars that retain leaves after head senescence. The corolla shedding period per head was longer than the 3.5 days per head reported b y Browne (1978). The period from first to last anther appearance in these trials was 9 days per head. Consequently, shedding of disk corollas might extend to 9 days if shedding indicates physiological maturity. Retention of disk corollas at early maturity for USDA 894, USDA 903, and USDA 924 was 61, 51, and 25%, respectively. Corolla retention was the same at both populations of USDA 894 and USDA 924 b u t was much higher at 25,000 plants per ha than at 49,000 plants per ha of USDA 903. Insects and other environmental factors also may prolong the corolla shedding period.
37
Whole plot studies Sunflower heads were a b o u t 80% water at the time their backs started to lose chlorophyll and turn yellow (Table II). Moisture loss was rapid for several weeks, b u t heads from completely brown plants averaged from 19 to 45% water. TABLE II Average performance of sunflower cultivars harvested at various stages of maturation in 1970 through 1972 Planting to harvest (days)
Maturation stage
Backs of heads 5% yellow 107 a Backs of heads 35% yellow 111 Backs of heads 75% yellow 117 Backs of heads 100% yellow 122 Stalks 50% brown 135 Plants 100% brown LSD (0.05)**
Aehene Head water (%)
Yield (kg/ha)
Test weight (kg/hl)
Weight/ Oil 100 (%) (g)
Large (%)
80
2,011
29.3
5.5
31.4
53
78
2,425
33.4
6.1
35.3
48
74
2,685
35.4
6.5
37.0
50
67 57
2,630 2,902
36.8 38.3
6.6 6.8
37.6 37.5
43 46
29 2
2,769 135
38.7 0.7
7.0 0.2
37.4 0.9
49 4
105 a
a1970--1971 data adjusted to be comparable with 1970--1972 data (Patterson, 1950). **F significant at 0.01 level.
Maximum achene yield occurred 5 days after the backs of the heads were 100% yellow. Test weight and achene weight also increased after the 100% yellow stage. Achene oil percentage did n o t increase significantly after the backs of the heads were 75% yellow. Achene size was determined before the maturation period because large seed percentage did not increase after the first harvest date. All cultivars responded alike to harvest at the maturation stages in Table II. The mean squares for the interactions of maturation stages X cultivars for all variables each year were either nonsignificant or significantly less than the mean squares for maturation stages. Maximum achene development was achieved earlier in the individual head (Table I) than in the whole plot (Table II) studies. Later-than-average plants do n o t reach their yield potential when time o f harvest is based on sampling of average plants. Consequently, the proportion of late plants is an important factor in choosing a time for desiccant application.
38
Drying sunflower plants in windrows or shocks might be an alternative to spraying with desiccants to permit early harvesting. Sunflower cut before physiological maturity might continue achene development while the plants cure. Whole plant harvesting would also enhance the feasibility of using stalks for phytomass, acoustical tile, and construction cores (MacGregor, 1970). There were no significant differences in yield or other achene characteristics between windrow-dried plants and oven-dried heads of sunflower harvested on the same days (Table III). These results indicate that achene development stopped when the stalks were severed. TABLE
III
Comparison of achenes from windrow- and oven-dried sunflower heads that were harvested at the same time
Head maturation stage
Backs 5% yellowa Backs 25% yellow a Backs 40% yellow Backs 80% yellow Backs 100% yellow Backs 35% brown CV (1970) CV (1971)
Windrow-dried/oven-dried
Yield (%)
Weight (%)
Oil (%)
97 101 106 100 97 94 7 14
102 103 100 103 100 100 4 17
101 101 100 99 100 100 2 11
a1971; other stages are from the 1970 crop.
CONCLUSIONS
Sunflower achenes reached physiological maturity when the backs of the heads were yellow. The interval between physiological maturity and brown senescence averaged 10, 13, 14, and 18 days for 4 years. Leaf loss and shedding of disk corollas were not reliable indicators of maturity. Sunflower plots harvested when average heads reached maturity suffered yield loss because of reduced yields from later-than-average plants. Sunflower achenes did not continue development after the stalks were severed. REFERENCES Anderson, W.K., 1975. Maturation of sunflower. Aust. J. Exp. Agric. Anim. Husb., 15: 833--838. Browne, C.L., 1978. Identification of physiological maturity in sunflowers (Helianthus annuus). Aust. J. Exp. Agric. Anita. Husb., 18: 282--286.
39 MacGregor, D., 1970. Formulation of new sunflower seed products. Proc. Int. Sunflower Conf., 9: 107--109. Patterson, R.E., 1950. A method of adjustment for calculating comparable yields in variety tests. Agron. J., 42: 509--511. Robertson, J.A., Chapman, G.W., Jr. and Wilson, R.L., Jr., I978. Relation of days after flowering to chemical composition and physiological maturity of sunflower seed. J. Am. Oil Chem. Soc., 55: 266--269. Robinson, R.G., 1971. Sunflower phenology -- year, variety, and date of planting effects on day and growing degree-day summations. Crop Sci., 11: 635--638. Robinson, R.G., Bernat, L.A., Geise, H.A., Johnson, F.K., Kinman, M.L., Mader, E.L., Oswalt, R.M., Putt, E.D., Swallers, C.M. and Williams, J.H., 1967. Sunflower development at latitudes ranging from 31 to 49 degrees. Crop Sci., 7: 134--136.
31
Elsevier Science Publishers B.V., Amsterdam - - Printed in The Netherlands
MATURATION OF SUNFLOWER AND SECTOR SAMPLING OF HEADS TO MONITOR MATURATION
R O B E R T G. R O B I N S O N
Department of Agronomy and Plant Genetics, University of Minnesota, St. Paul, MN 55108 (U.S.A.) Minnesota Agricultural Experiment Station Scientific Journal Series paper 11,400. (Accepted 5 January 1983)
ABSTRACT Robinson, R.G., 1983. Maturation of sunflower and sector sampling of heads to monitor maturation. Field Crops Res., 7: 31--39. Research was undertaken to relate visual appearance of sunflower (Helianthus annuus L.) plants with achene maturation and to determine if severing stalks before physiological maturity stops achene growth. A new technique for studying maturation involved harvesting sectors of achenes at different times from the same head receptacle and determining weight per 100 achenes. Economic physiological maturity occurs at the stage when achenes reach maximum weight. These individual head studies with diverse cultivars and plant populations showed that maturity occurred after backs of heads were completely yellow. Leaf loss was not a reliable indicator of physiological maturity. Each year, about 1350 growing degree-days (GDD) occurred between planting and physiological maturity. The interval between physiological maturity and brown senescence of heads averaged 10, 13, 14, and 18 days for 4 years. Whole plot studies showed that the accuracy of maturation ratings based on average heads may be affected by later-than-average heads. Sunflower heads were about 80% water at the initiation of yellowing and 19 to 45% water at brown senescence. Achene size was determined before head yellowing whereas yield, oil percentage, weight/hi, and weight per-achene increased during the maturation period. Achenes from severed plants dried in the field and from heads harvested the same day but dried in an oven did not differ in yield or other characteristics indicating that achene development stops when stalks are cut.
INTRODUCTION
Five growth periods of six sunflower (Helianthus annuus L.) Cultivars averaged 11 days from planting to emergence, 33 days from emergence to head visible, 27 days from head visible to first anthesis, 8 days from first to last anthesis, and 30 days to physiological maturity over a 3-year period (Robinson, 1971). All stages can be identified precisely except physiological maturity. Consequently, maturity is estimated visually by the change from green to yellow coloration of the backs of the heads and involucral bracts. Backs of the heads and stalks become brown as senescence proceeds. 0378-4290/83/$03.00
© 1983 Elsevier Science Publishers B.V.
32 Anderson (1975) defined physiological maturity as the time when achene dry weight, oil percentage, and linoleic acid percentage reach their maximum. At that time, the backs of heads were yellow b u t 10% were brown, and the achenes were 40% water. Robertson et al. (1978) harvested heads at weekly intervals from 7 to 70 days after first anthesis. Maximum achene weight and oil percentage occurred 35 days after first anthesis when achenes were 36% water. This research embraced one cultivar for 1 year, and the authors sampled only the achenes from the outer 3 to 7 cm of the heads. Browne (1978) sampled 10 achenes, from the radial arcs of VNIIMK 6540 cultivar at various dates and found that the achenes reached maximum dry weight 31 days after last anthesis when achene moisture was 29%. This stage occurred in the middle of the 3.5 day interval between the first and last abscission of the diskflorets (corollas and enclosed stigma, style, and stamen remnants). The objectives of this research were to: ascertain lengths of some maturation periods between the initiation of head yellowing and brown senescence; determine if head yellowing is a reliable indicator of physiological maturity; and find o u t if severing the stalks before physiological maturity stops achene growth. MATERIALS AND METHODS Trials were c o n d u c t e d on Typic Hapludoll~ fine silty over sandy or sandyskeletal, mixed, mesic (Waukegan silt loam) soil at Rosemount, MN. R o w spacings were 102 cm in 1970 and 1971 and 76 cm in 1972 and 1980. Separate trials involved individual plants and bulked plants from whole plots. Individual head studies Arrowhead and Mingren nonoilseed cultivars and Peredovik and P-21ms X HA 60 oilseed cultivars were planted 3 May 1970, 2 May 1971, and 4 May 1972. Nonoilseed cultivar USDA 924 and oilseed cultivars USDA 894 and USDA 903 were planted 5 May 1980. Arrowhead, Mingren, and Peredovik are n o t hybrids; the other cultivars are single-cross hybrids. Plant populations for all cultivars were 57,000 plants per ha in 1970 through 1972 and 49,000 and 25,000 plants per ha in 1980. Achenes from the same head were harvested at three stages of maturation from receptacle sectors of 12 to 15 heads of each cultivar at each population (Fig. 1). All achenes in a sector were taken except those along the exposed edge of the previous sector. Heads with sectors of achenes removed continued to mature like nearby unsampled heads. Maturation stages included: premature -- backs of heads and involucral bracts greenish yellow to yellow; early maturity -- backs of heads and involucral bracts 90 to 100% yellow; and early senescence -- backs of heads and involucral bracts 95 to 100% brown. Each sample of achenes was placed in a separate plastic bag and later,
33
Fig. 1. Immature sunflower head with disk flower corollas removed from one sector (A) exposing the achenes and the achenes removed from another sector (B) exposing the receptacle.
the same day, passed through a fanning mill to remove sterile achenes. Fertile achenes were weighed, dried at 70°C for 4 days, and then dried at 100°C for 4 h and weighed again to allow calculation of achene moisture percentage. Variables measured for each sector on each head included achene moisture and oil percentages, weight per 100 achenes, and growing degree-day (GDD) summations between date of planting or first anthesis to date of harvest. Oil percentages were determined at the University of Illinois with nuclear magnetic resonance equipment. Daffy maximum and minimum temperatures were taken from an official weather station a b o u t 1 km away. GDD for each d a y in centrigrade units were calculated by averaging the minimum and m a x i m u m temperatures and subtracting 7.2°C base temperature (Robinson et al., 1967). Trials for each o f first 3 years were analyzed as randomized blocks using heads, cultivars, sectors (maturation stages), and cultivars X sectors as components of variation and interactions with heads as error. The 1980 trial was analyzed as a split split-plot with heads, cultivars, populations, cultivars × populations, sectors, cultivars × sectors, populations X sectors, and cultivars × populations × sectors as components of variation and appropriate interactions with heads as error.
34 TABLE I Average o f f o u r s u n f l o w e r cultivars in 1 9 7 0 , 1 9 7 1 , a n d 1 9 7 2 a n d o f t h r e e cultivars in 1 9 8 0 f o r weight, oil p e r c e n t a g e , a n d m o i s t u r e p e r c e n t a g e o f a c h e n e s r e m o v e d f r o m t h e h e a d s a t t h r e e stages o f m a t u r a t i o n a a n d d a y a n d g r o w i n g degree-day ( G D D ) s u m m a t i o n at t h e s e stages 1970
1971
1972
1980
A c h e n e w e i g h t / 1 0 0 (g) Premature Early maturity Early senescence LSD ( 0 . 0 5 )
7.2 7.3 7.5 0.3
7.9 9.0 9.1 0.2**
6.5 7.0 7.3 0.4**
32.4 32.6 32.5 1.1
31.9 34.2 34.7 2.0**
33.5 34.7 34.6 1.3
39.6 33.6 11.9 5.1"*
54.0 41.3 14.1 2.4**
54.8 44.4 18.2 2.4**
-7.2 7.1 0.1"*
A c h e n e oil (%) Premature Early maturity Early senescence LSD (0.05)
-----
A c h e n e w a t e r (%) Premature Early maturity Early senescence LSD ( 0 . 0 5 )
-36.6 16.0 1.2"*
Planting to achene removal (days) Premature Early maturity Early senescence
106 111 121
107 113 131
106 112 126
-114 127
1342 1409 1549
1169 1253 1484
1209 1293 1452
-1445 1620
31 38 56
30 36 50
-43 56
373 456 688
392 477 635
-617 785
Planting to achene removal (GDD) Premature Early maturity Early senescence F i r s t a n t h e s i s t o a c h e n e r e m o v a l (days) Premature Early maturity Early senescence
--
---
First anthesis to achene removal (GDD) Premature Early maturity Early senescence
--
---
a p r e m a t u r e - - b a c k s o f h e a d s greenish y e l l o w t o yellow. E a r l y m a t u r i t y - - b a c k s o f h e a d s 9 0 t o 1 0 0 % yellow. E a r l y s e n e s c e n c e - - b a c k s o f h e a d s 9 5 t o 100% b r o w n . * * F s i g n i f i c a n t at 0 . 0 1 level.
35
Whole plot studies Arrowhead and Mingren nonoilseed cultivars plus Peredovik and P-21ms × HA 60 oilseed cultivars were planted 3 May 1970 and 1 May 1971. Oilseed hybrid cultivars P-21ms × HA 60 and cmsHA 93 X R H A 265 were planted 4 May 1972. Whole heads were harvested at five stages of maturation in 1970 and six stages o f maturation in 1971 and 1972. Maturation stages ranged from disk corollas remaining and head yellowing to brown senescence (Table II). Split-plot experimental designs involved cultivars replicated three times as main plots and maturation stages as subplots. Subplots were three rows 6 m long. A 5-m length of the center row was harvested to measure head moisture percentage and achene yield per ha. Heads were severed close to the receptacle, weighed, dried at 70°C for 3 weeks, weighed again, and head moisture percentage calculated. Heads were threshed and achene yield, test weight, weight/100, oil percentage, and large size percentage determined. Large achene percentage was measured b y sieving 100-g samples. Achenes held on 0.79, 0.64, 0.56, 0.56, and 0.48 cm round-hole screens were considered large for Mingren, Arrowhead, Peredovik, P-21ms × HA 60, and cmsHA 93 × R H A 265, respectively. Additional subplots were included for all treatments in 1970 and for the first t w o maturation stages in 1971. On these subplots, stalks were cut 20 cm above the soil to simulate a windrower or corn binder. A 5-m length of each center row was left to dry in a windrow. After drying to less than 15% achene moisture, heads were severed from the stalks, dried at 70 ° C, and processed like the other treatments. RESULTS AND DISCUSSION
Individual head studies Achene yield o f a sunflower head is the product of the number of fertile achenes and the weight per fertile achene. Since the number of fertile achenes is determined prior to maturation, m a x i m u m yield occurs when the fertile achenes reach their m a x i m u m weight. Significant increases in achene weights and achene oil percentages did n o t occur after 111 days from planting in 1970, 113 days in 1971, 112 days in 1972, and 114 days in 1980 (Table I). Consequently, achenes at these dates were near physiological maturity, and achene moisture percentages averaged from 34 to 44% among years. Backs o f the heads and involucral bracts were 90 to 100% yellow at this stage. Cultivars differed in maturity, head type, achene size, achene oil percentage, disease resistance, leaf retention, and disk corolla retention. Despite these differences, mean squares for the interactions of maturation stages X cultivars and maturation stages × populations were either nonsignificant or
36 significantly less than the mean squares for maturation stages. Consequently average data are shown in Table I. Day and GDD summations are two c o m m o n methods of designating maturity of corn {Zea mays L.) and pea (Pisum sativum L.). GDD summations are usually less variable among years than are day summations, so they are used by the canning industry to predict harvest time for individual fields. Robinson et al. (1967) used four different base temperatures for GDD summations between planting and anthesis for eight sunflower cultivars at nine locations ranging from 31 to 49 degrees latitude in North America. They concluded that any reasonable base temperature was satisfactory for comparisons within a narrow range of latitudes. The 7.2°C base temperature used in this research lies between the 10°C base for corn and the 4.4°C base for pea. Day and GDD summations from planting and from first anthesis to early maturity and to early senescence were useful b u t n o t precise predictors of maturation stages. Data in Table I do n o t support using date of first anthesis rather than date of planting to begin day or GDD summations to maturity. In 1980, 87% o f the upper leaves were still green at early maturity and then declined to only 4% green leaves at early senescence. Leaf retention was much less in the first 3 years with nonhybrid cultivars. Hybrid cultivars and populations also differed significantly in leaf retention. Green leaf retention at early maturity was 22% greater for the 25,000 plant/ha population. Consequently, leaf loss was n o t a reliable indicator of physiological maturity. Preharvest desiccants are used to kill sunflower and advance senescence to the b r o w n stage more rapidly than it occurs naturally. The time between the start of physiological maturity and brown senescence was 10 days in 1970, 18 in 1971, 14 in 1972, and 13 in 1980 (Table I). Sunflower plants do n o t become completely brown for at least 2 days after spraying, and it is illegal to harvest within 7 days of spraying. Consequently, the potential advance in senescence from spraying the average head was n o t great. However, desiccants may advance harvest date considerably in fields with heads in various stages of maturation or with cultivars that retain leaves after head senescence. The corolla shedding period per head was longer than the 3.5 days per head reported b y Browne (1978). The period from first to last anther appearance in these trials was 9 days per head. Consequently, shedding of disk corollas might extend to 9 days if shedding indicates physiological maturity. Retention of disk corollas at early maturity for USDA 894, USDA 903, and USDA 924 was 61, 51, and 25%, respectively. Corolla retention was the same at both populations of USDA 894 and USDA 924 b u t was much higher at 25,000 plants per ha than at 49,000 plants per ha of USDA 903. Insects and other environmental factors also may prolong the corolla shedding period.
37
Whole plot studies Sunflower heads were a b o u t 80% water at the time their backs started to lose chlorophyll and turn yellow (Table II). Moisture loss was rapid for several weeks, b u t heads from completely brown plants averaged from 19 to 45% water. TABLE II Average performance of sunflower cultivars harvested at various stages of maturation in 1970 through 1972 Planting to harvest (days)
Maturation stage
Backs of heads 5% yellow 107 a Backs of heads 35% yellow 111 Backs of heads 75% yellow 117 Backs of heads 100% yellow 122 Stalks 50% brown 135 Plants 100% brown LSD (0.05)**
Aehene Head water (%)
Yield (kg/ha)
Test weight (kg/hl)
Weight/ Oil 100 (%) (g)
Large (%)
80
2,011
29.3
5.5
31.4
53
78
2,425
33.4
6.1
35.3
48
74
2,685
35.4
6.5
37.0
50
67 57
2,630 2,902
36.8 38.3
6.6 6.8
37.6 37.5
43 46
29 2
2,769 135
38.7 0.7
7.0 0.2
37.4 0.9
49 4
105 a
a1970--1971 data adjusted to be comparable with 1970--1972 data (Patterson, 1950). **F significant at 0.01 level.
Maximum achene yield occurred 5 days after the backs of the heads were 100% yellow. Test weight and achene weight also increased after the 100% yellow stage. Achene oil percentage did n o t increase significantly after the backs of the heads were 75% yellow. Achene size was determined before the maturation period because large seed percentage did not increase after the first harvest date. All cultivars responded alike to harvest at the maturation stages in Table II. The mean squares for the interactions of maturation stages X cultivars for all variables each year were either nonsignificant or significantly less than the mean squares for maturation stages. Maximum achene development was achieved earlier in the individual head (Table I) than in the whole plot (Table II) studies. Later-than-average plants do n o t reach their yield potential when time o f harvest is based on sampling of average plants. Consequently, the proportion of late plants is an important factor in choosing a time for desiccant application.
38
Drying sunflower plants in windrows or shocks might be an alternative to spraying with desiccants to permit early harvesting. Sunflower cut before physiological maturity might continue achene development while the plants cure. Whole plant harvesting would also enhance the feasibility of using stalks for phytomass, acoustical tile, and construction cores (MacGregor, 1970). There were no significant differences in yield or other achene characteristics between windrow-dried plants and oven-dried heads of sunflower harvested on the same days (Table III). These results indicate that achene development stopped when the stalks were severed. TABLE
III
Comparison of achenes from windrow- and oven-dried sunflower heads that were harvested at the same time
Head maturation stage
Backs 5% yellowa Backs 25% yellow a Backs 40% yellow Backs 80% yellow Backs 100% yellow Backs 35% brown CV (1970) CV (1971)
Windrow-dried/oven-dried
Yield (%)
Weight (%)
Oil (%)
97 101 106 100 97 94 7 14
102 103 100 103 100 100 4 17
101 101 100 99 100 100 2 11
a1971; other stages are from the 1970 crop.
CONCLUSIONS
Sunflower achenes reached physiological maturity when the backs of the heads were yellow. The interval between physiological maturity and brown senescence averaged 10, 13, 14, and 18 days for 4 years. Leaf loss and shedding of disk corollas were not reliable indicators of maturity. Sunflower plots harvested when average heads reached maturity suffered yield loss because of reduced yields from later-than-average plants. Sunflower achenes did not continue development after the stalks were severed. REFERENCES Anderson, W.K., 1975. Maturation of sunflower. Aust. J. Exp. Agric. Anim. Husb., 15: 833--838. Browne, C.L., 1978. Identification of physiological maturity in sunflowers (Helianthus annuus). Aust. J. Exp. Agric. Anita. Husb., 18: 282--286.
39 MacGregor, D., 1970. Formulation of new sunflower seed products. Proc. Int. Sunflower Conf., 9: 107--109. Patterson, R.E., 1950. A method of adjustment for calculating comparable yields in variety tests. Agron. J., 42: 509--511. Robertson, J.A., Chapman, G.W., Jr. and Wilson, R.L., Jr., I978. Relation of days after flowering to chemical composition and physiological maturity of sunflower seed. J. Am. Oil Chem. Soc., 55: 266--269. Robinson, R.G., 1971. Sunflower phenology -- year, variety, and date of planting effects on day and growing degree-day summations. Crop Sci., 11: 635--638. Robinson, R.G., Bernat, L.A., Geise, H.A., Johnson, F.K., Kinman, M.L., Mader, E.L., Oswalt, R.M., Putt, E.D., Swallers, C.M. and Williams, J.H., 1967. Sunflower development at latitudes ranging from 31 to 49 degrees. Crop Sci., 7: 134--136.