- Email: [email protected]
General and specific combining ability estimates for pith cell death in stalk internodes of maize
Field Crops Research, 17 (1987) 155-161
155
Elsevier Science Publishers B.V., Amsterdam - - Printed in The Netherlands
General and Specific Combining Ability Estimates for Pith Cell Death in Stalk Internodes of Maize T.R. C O L B E R T I,M.S. K A N G 2,O. M Y E R S a and M.S. Z U B E R 4
1Funk Seeds International, Union City, TN 38261 (U.S.A.) 2Department of Agronomy, Louisiana Agricultural Experiment Station, Louisiana State University Agricultural Center, Baton Rouge, LA 70803-2110 (U.S.A.) 3Department of Plant and Soil Science, Southern Illinois University, Carbondale, IL 62901 (U.S.A.) 4Department of Agronomy, University of Missouri, Columbia, MO 65211 (U.S.A.) (Accepted 21 April 1987)
ABSTRACT
Colbert, T.R., Kang, M.S., Myers, 0. and Zuber, M.S., 1987. General and specific combining ability estimates for pith cell death in stalk internodes of maize. Field Crops Res., 17: 155-161. Stalk rot and associated stalk lodging in maize (Zea mays L.) continue to be major production problems, The inheritance of several stalk traits that contribute to stalk strength has been studied previously. However, inheritance of pith (parenchyma) cell death, an important stalk quality trait, has not been thoroughly investigated. The objective of this study was to estimate general and specific combining ability effects for pith cell death through a diallel mating design. All possible crosses among six inbred lines (C103, Mol7, B14A, W64A, WIg, and B37) were evaluated at two locations and analyzed according to Griffing's method 2, model 1 (fixed effects for genotypes). General combining ability effects were found to be more important than specific combining ability effects. Heritability of F1 hybrid means was estimated to be 86%. A cyclic selection program might be effective in reducing pith cell death. A reduction in pith cell death would result in stalk-rot resistance which is positively correlated to the presence of living cells in the stalk.
INTRODUCTION
Improving stalk quality in maize (Zea m a y s L. ) has been a continuing challenge to maize breeders as stalk lodging continues to be a major production problem. Stalk rot and associated stalk lodging result in yield losses of 5-25% annually (Zuber, 1973; Zuber and Kang, 1978), Various techniques have been developed to identify and select maize genotypes with superior stalk quality ( Cloninger et al., 1970). A stalk-crushing method described by Zuber and GroNote: Approved for publication by the Director of the Louisiana Agricultural Experiment Station as manuscript number 87-09-1193. Please address reprint requests to Dr. Kang.
0378-4290/87/$03.50
© 1987 Elsevier Science Publishers B.V.
156
gan (1961) has been successfully used to improve stalk quality through several cycles of recurrent selection (Zuber, 1973). Inheritance and procedures for improvement of three important stalk-quality traits, viz., crushing strength, weight of stalk section, and rind thickness, have been reported by several researchers (Loesch et al., 1963; Singh et ah, 1969; Loesch, 1972; Zuber, 1973; Zuber and Kang, 1978; Kang et al., 1979 ). Effects of selection for high and low stalk-crushing strength in two maize synthetics on anatomical features of stalks (Berzonsky et al., 1986) and on agronomic characteristics (Zuber, 1973; Colbert et al., 1984; Berzonsky and Hawk, 1986) have been studied. In addition to the three stalk-quality traits mentioned above, pith (parenchyma) cell death in stalk internodes has been implicated as an important stalk-quality trait (BeMiller and Pappelis, 1965; Pappelis and Williams, 1966; Pappelis et ah, 1971; Kang et al., 1974; Kang et al., 1986). Pappelis ( 1957 ) discoveredthat stalk rot incited by Diplodia maydis (Berk.) Sacc. was related to the death of parenchyma cells in the stalk, and stalk rot resistance was related to the presence of living cells in that tissue. The relationship of pith condition to the spread of stalk-rotting fungi has been studied by several researchers (Craig and Hooker,,1961; Pappelis and Smith, 1963; Pappelis and Williams, 1966; Wysong and Hooker, 1966; Gates, 1970; Pappelis, 1970; Pappelis et al., 1971; Kang et ah, 1974). A highly significant positive correlation between pith cell death and stalk rot ratings was reported by Pappelis and Williams {1966). A decrease in soluble solids in stalks is associated with an increase in stalk lodging due to higher pith cell death and stalk rot ( Craig and Hooker, 1961 ). Pappelis and Katsanos (1969) reported that ear removal resulted in delayed cell death in stalk internodes. Kang et al. {1974) inoculated the cob and shank with D. maydis about 10 days after silking and demonstrated that these inoculations delayed cell death in stalk internodes. Later, Dodd (1977, 1980) proposed the photosynthetic stress-translocation balance hypothesis of predisposition of maize to stalk rot, i.e., any factor that affected ear (sink size) or translocation efficiency would be implicated in stalk rot. However, Schneider and Pendery (1983) have questioned Dodd's hypothesis on the basis that Dodd reported no determinations of stalk condition, rates of photosynthesis or translocation, pith density, water relations or other stress-related physiological processes. Schneider and Pendery (1983) suggested that stress factors that might act as a predisposing agent must be studied separately before a unifying concept can be developed. The relative contributions of rind and pith to total stalk strength are approximately 60 and 40%, respectively (Zuber and Kang, 1978). Pith cell death was found to be negatively correlated with crushing strength and rind thickness of 5-cm-long sections from the second stalk internode (Miller and Myers, 1974). However, inheritance of pith cell death has not been thoroughly investigated. A study involving reciprocal chromosomal interchanges (M.S. Kang, 1987, unpublished data from two locations) indicated that gene loci condition-
157 ing pith cell death in stalk internodes of maize might be many in number and located on several different chromosomes. However, no quantitative genetic study of this trait has been made. The objective of this study was to estimate general and specific combining ability effects for pith cell death through a diallel mating design. MATERIALS AND METHODS
Six inbred lines of maize (C103 and Mo17, low cell death; B14A, W64A and Wf9, intermediate cell death; and B37, high cell death) were crossed in all possible combinations. The resulting 15 F1 hybrids or single crosses were selfed to obtain F2 populations. The parents, F1 hybrids, and F2 populations were planted at the Agronomy Research Farm, Southern Illinois University at Carbondale, Ill., and the Rollins Bottom Maize Nursery, University of Missouri at Columbia, Mo., on June 1 and May 27, 1971, respectively. At each location, a randomized complete block design with three replications was used. The inbreds and F~ hybrids were planted in single-row plots of 5 m length, with 13 plants per row. The rows were spaced 96.5 cm apart, and the plant-to-plant spacing within row was 33 cm. The F2 populations were grown in similar tworow plots. Mid-silking dates for all plots were recorded. Stalks from 13 plants of inbreds and F~ hybrids, and 26 plants of F2 populations were split longitudinally, one day after their respective mid-silking dates. Five consecutive elongated internodes above the brace roots were visually evaluated for pith cell death using the following rating scale developed by Pappelis (1957): 0.0, no white tissue (dead cells) in the pith; 0.1, less than 1% white; 0.5, 2-12% white; 1.0, 13-25% white; 2.0, 26-50% white; 3.0, 51-75% white; 4.0, 76-100% white; 5.0, same as 4.0 with white tissue in the node linking adjacent internodes; and 6.0, same as 5.0 but plant dead. Plot means (mean rating of five internodes per plant over all plants in a plot) were used to estimate general combining ability (GCA) and specific combining ability (SCA) components according to Griffing's (1956) method 2, model 1 (genotypes being fixed effect). Locations were regarded as random effect. The least significant difference (LSD) values were used to test differences among means of inbreds, F1 hybrids, F2 populations, line means (F~), and estimated GCA effects ($i). Mid-parent values for the 15 F~ hybrids were calculated and a rank-correlation coefficient between F1 mean ratings and the mid-parent values was determined. Heritability (broad-sense) among F1 hybrid means was estimated as follows: H = a~l 2 2 2 / ( a~l + a21 × LJl + aeJrZ) where H = heritability (broad-sense), a~l = F1 variance component, aF,2× L / 1 = F~ by location interaction component, a2/rl = error variance component, l= no. of locations, and r = no. of replications.
158
TABLE 1 Combined analysis of variance for pith cell death ratings from Carbondale, Illinois, and Columbia, Missouri Source of variation
(if
Mean square
Locations (L) Replications: L Genotypes (G) Inbreds (I) Single crosses (F1)
1 4 35 5 14 5 9 14 2 35 5 14 5 9 14 2 140
2.494 0.588** 0.885** 1.678"* 0.517"* 1.245"* 0.112 0.769** 2.292 0.O82 O.O94 0.073 0.075 O.O72 0.032 0.066 0.054
GCA SCA F2 populations (F2)
Generations (Gen) L× G L× I L × F1 L × GCA L X SCA L × F2 L X Gen
Pooled error
**Significant at the 1% level of probability. RESULTS AND DISCUSSION
A combined analysis of variance for pith cell death is shown in Table 1. Mean squares for inbreds, FI hybrids, F2 populations, and GCA effects were significant. Replications-within-location effect also was significant. The remainder of effects were not significant at the 5% level. The GCA effects accounted for 86% of the corrected sum of squares among F1 hybrids and the other 14% were attributable to SCA effects, indicating that the GCA effects were much more important that the SCA effects in the six inbreds studied. A study by Arnold and Josephson (1975) of percentage of senescent (dead) stalks also indicated that additive genetic effects were more important than non-additive genetic effects. However, their study did not consider the amount of dead cells in each stalk. Mean cell death ratings for the parental inbred lines~ F1 hybrids, and F2 populations are given in Table 2. Mid-parent values ( M P ) , line means (F1), and estimates of GCA effects for the inbred lines are also shown in Table 2. Mean pith cell death of C103, Mo17, and B14A was significantly lower than that of W64A, Wf9, and B37. Mo17 × C103, a single cross involving two inbred lines with low pith cell death, had the lowest pith cell death of all the FI hybrids. Wf9 × B37 had the
159 TABLE 2 Mean pith cell death ratings of F1 hybrids {abovediagonal ), inbreds (diagonal), F2 populations (below diagonal), mid-parent value (in parenthesis, above diagonal), line means of F~ hybrids ( i~ ) and of mid-parent values (MP), and GCA effects of parental lines C103 Mol7
B 1 4 A W 6 4 A Wi0
B37
F1
MP
GCA effect (gi)
C103
1.53 1.56
B14A
1.37
2.12
2.06 (1.63) 2.23 (1.65) 1.72
W64A 2.28
2.35
2.37
2.47 (1.90) 2.24 (1.93) 2.58 (2.00) 2.27
Wf9
2.07
2.23
2.24
2.48
2.46 (1.92) 2.49 (1.95) 2.61 (2.02) 2.64 (2.29) 2.31
B37
2.10
2.23
2.37
2.65
2.75
2.15 (2.21) 2.47 (2.23) 2.70 (2.30) 2.65 (2.58) 2.98 (2.60) 2.88
2.19 1.84 -0.31
Mo17
1.82 (1.56) 1.58
2.25 1.86 -0.23 2.44 1.92
0.00
2.52 2.14
0.10
2.64 2.16
0.25
2.59 2.38
0.19
Overall means: F1 hybrids = 2.44; F2 populations = 2.21; Inbreds = 2.04. LSD~o.os) for testing differences among. F~ hybrids=0.31; F2 populations=0.33; Inbreds=0.35; F1 - F2= 0.34; i~1= 0.14; ~i= 0.087; ~i-$j = 0.095. highest pith cell death. Ten of the 15 F1 hybrids had higher ratings than the higher pith-cell-death parent, three F1 hybrids were nearly equal to the higher parent, and two were close to their mid:parent values. All the F1 hybrids except C103 X B37 had higher cell-death ratings than their respectivemid-parent values. A rank-correlation coefficient of 0.84 (significant at the 1% level) was found between the cell-death ratings of the F~ hybrids and their corresponding mid-parent values, which suggested that mid-parent values could serve as a reasonable predictor of F1 hybrid cell-death ratings. Four of the six mean midparent values and line means had the same rank, indicating that the M P might be useful in predicting line means or single-cross performance. However, the estimates of GCA effects of the six inbred lines were in the same rank order as the line means, indicating that the use of GCA effects would be better in predicting cell death ratings of F~ hybrids than would mid-parent values. Furthermore, Baker (1978) pointed out that the performance o f a single-cross progeny can be adequately predicted on the basis of general combining ability when specific combining ability mean square is not significant. Gilbert (1958) also indicated that main effects estimated by diallel analysis gave a better prediction than did a regression on mid-parent, taking into account the fact that general combining ability is measured with greater precision than is mid-parent value. The GCA effects of C 103 and Mo17 were negative; of B14A negligible; and of Wf9, B37, and W64A, positive. The use of C103 and Mo17 in breeding pro-
160 grams might be effective in reducing pith cell death and possibly stalk rot and associated stalk lodging. Heritability of F1 hybrid means was estimated to be 86%. The magnitude of GCA effects relative to SCA effects suggested t h a t broadsense heritability of pith cell death would approximate narrow-sense heritability and was mainly due to additive genetic effects. These results, although limited in scope because of the small number of parents involved, indicated that a cyclic selection program might be effective in reducing the a m o u n t of cell death in stalks of maize, thus improving stalk strength. Among individual F1 and F2 comparisons, F2 means were lower than F~ means in all cases except Mo17 × W64A. In three cases, i.e., C103 × B14A, C103 × Wfg, and B 14A × Wf9, the F2 means were significantly lower t h a n the corresponding F1 means, indicating an inbreeding depression characteristic of non-additive gene action. However, the parental lines of the remaining 11 single crosses contributed mainly additive genetic effects as their F2 means were not significantly different from their F1 means. Since pith cell death and spread of stalk-rotting fungi are closely related (Pappelis et al., 1971) and because pith contributes to total stalk strength (Zuber and Kang, 1978), a reduction in pith cell death might cause a corresponding reduction in incidence of stalk rot. Cell death in stalk internodes is measured with ease in the field, The rating system used in the evaluation of pith cell death has been shown to be reasonably precise (Pappelis and Williams, 1966; Pappelis and Katsanos, 1969). Desirable lines may be identified in the field on the basis of a sample of about five plants of inbreds or single crosses. Such identification is possible prior to flowering, thus making it possible to cross the desired lines in the same generation. Selection for low pith cell death could result in stalk-rot resistant plants, as living, hydrated pith cells characterize stalks resistant to Diplodia maydis stalk rot.
REFERENCES Arnold, J.M. and Josephson, L.M., 1975. Inheritance of stalk-quality characteristics in maize. Crop Sci., 15: 338-340. Baker, R.J., 1978. Issues in diallelanalysis. Crop Sci., 18: 533-536. BeMiller, J.N. and Pappelis, A.J., 1965.2-4-Dihydroxy-7-methoxy-1,4-benzoxazin-3-oneglycoside in corn. I. Relation of water-soluble 1-butanol-solubleglucosidefraction content of pith cores and stalk rot resistance. Phytopathology,55: 1237-1240. Berzonsky, W.A. and Hawk, J.A., 1986. Agronomicfeatures of two maize synthetics selected for high and low stalk-crushing strength. Crop Sci., 26: 871-875. Berzonsky,W.A.,Hawk,J.A. and Pizzolato,T.D., 1986. Anatomicalcharacteristicsof three inbred lines and two maize synthetics recurrently selected for high and low stalk-crushing strength. Crop Sci,, 26: 482-488. Cloninger, F.D., Zuber, M.S., Calvert, O.H. and Loesch, P.J., Jr., 1970. Methods of evaluating stalk quality in corn. Phytopathology,60: 295-300.
161 Colbert, T.R., Darrah, L.L. and Zuber, M.S., 1984. Effect of recurrent selection for stalk-crushing strength on agronomic characteristics and soluble solids in maize. Crop Sci., 24: 473-478. Craig, J. and Hooker, A.L., 1961. Relation of sugar trends and pith density to Diplodia stalk rot in corn. Phytopathology, 51: 376-382. Dodd, J.L., 1977. A photosynthetic stress-translocation balance concept of corn stalk rot. Proc. Annu. Corn Sorghum Res. Conf., 32: 122-130. Dodd, J.L., 1980. Grain sink size and predisposition ofZea mays to stalk rot. Phytopathology, 70: 534-535. Gates, L.F., 1970. Relationships between pith cell death conditions as assessed by tetrazolium chloride and incidence of GibbereUa stalk rot in corn. Can. J. Plant Sci., 50: 674-684. Gilbert, N.E.G., 1958. Diallel cross in plant breeding. Heredity, 12: 477-494. Griffing, B., 1956. Concept of general and specific combining ability in relation to diallel crossing systems. Aust. J. Biol. Sci., 9: 463-493. Kang, M.S., Pappelis, A.J., Mumford, P., Murphy, J.A. and BeMiller, J.N., 1974. Effect of cob and shank inoculations (Diplodia maydis) on cell death in stalk internodes of corn. Plant Dis. Rep., 58: 1113-1117. Kang, M.S., Zuber, M.S., Myers, O. and Colbert, T.R., 1979. Genetic studies on three stalk traits in maize using chromosomal interchanges. Can. J. Genet. Cytol., 21: 139-144. Kang, M.S., Pappelis, A.J. and Zuber, M.S., 1986. Effect of stalk inoculation (Diplodia maydis) on parenchyma cell death in cob and shank internodes of maize. Cereal Res. Commun., 14: 267-272. Loesch, P.J., Jr., 1972. Diallel analysis of stalk quality traits in 12 inbred lines of maize. Crop Sci., 12: 261-264. Loesch, P.J., Jr., Zuber, M.S. and Grogan, C.O., 1963. Inheritance of crushing strength and rind thickness in several inbred lines of corn. Crop Sci., 3: 173-174. Miller, T.L. and Myers, O., 1974. Correlation of pith cell death with various stalk quality characteristics in two synthetic populations of maize. Crop Sci., 14: 215-217. Pappelis, A.J., 1957. Nature of resistance to Diplodia stalk rot of corn. Ph.D. Thesis, Iowa State University, Ames, Ia., 204 pp. Pappelis, A.J., 1970. Effect of root and leaf injury on cell death and stalk rot susceptibility in corn. Phytopathology, 60: 355-357. Pappelis, A.J. and Katsanos, R.A., 1969. Ear removal and cell death rate in stalk tissue. Phytopathology, 59: 129-131. Pappelis, A.J. and Smith, F.G., 1963. Relationship of water content and living cells to spread of D iplodia zeae in corn stalks. Phytopathology, 53: 1100 - 1105. Pappelis, A.J. and Williams, J.R., 1966. Patterns of cell death in the elongating corn stalks. Trans. Ill. State Acad. Sci., 59: 195-198. Pappelis, A.J., BeMiller, J.N., Schmid, W.E., Myers, O. and Murphy, J.A., 1971. Stalk rot of corn. Proc. Annu. Corn Sorghum Res. Conf., 28: 110-122. Singh, T.P., Zuber, M.S. and Krause, G.F., 1969. Relationship of certain stalk characters with grain yield in corn (Zea mays L. ). Crop Sci., 9: 265-267. Schneider, R.W. and Pendery, W.E., 1983. Stalk xot of corn: mechanism of predisposition by an early-season water stress. Phytopathology, 73: 863-871. Wysong, D.S. and Hooker, A.L., 1966. Relation of soluble solids content and pith condition to Diplodia stalk rot in corn hybrids. Phytopathology, 56: 26-35. Zuber, M.S., 1973. Evaluation of progress in selection for stalk quality. Proc. Annu. Corn Sorghum Res. Conf., 28: 110-122. Zuber, M.S. and Grogan, C.O., 1961. A new technique for measuring stalk strength in corn. Crop Sci., 1: 378-380. Zuber, M.S. and Kang, M.S., 1978. Corn lodging slowed by sturdier stalks. Crop Soils, 30 (5)N: 13-15.
155
Elsevier Science Publishers B.V., Amsterdam - - Printed in The Netherlands
General and Specific Combining Ability Estimates for Pith Cell Death in Stalk Internodes of Maize T.R. C O L B E R T I,M.S. K A N G 2,O. M Y E R S a and M.S. Z U B E R 4
1Funk Seeds International, Union City, TN 38261 (U.S.A.) 2Department of Agronomy, Louisiana Agricultural Experiment Station, Louisiana State University Agricultural Center, Baton Rouge, LA 70803-2110 (U.S.A.) 3Department of Plant and Soil Science, Southern Illinois University, Carbondale, IL 62901 (U.S.A.) 4Department of Agronomy, University of Missouri, Columbia, MO 65211 (U.S.A.) (Accepted 21 April 1987)
ABSTRACT
Colbert, T.R., Kang, M.S., Myers, 0. and Zuber, M.S., 1987. General and specific combining ability estimates for pith cell death in stalk internodes of maize. Field Crops Res., 17: 155-161. Stalk rot and associated stalk lodging in maize (Zea mays L.) continue to be major production problems, The inheritance of several stalk traits that contribute to stalk strength has been studied previously. However, inheritance of pith (parenchyma) cell death, an important stalk quality trait, has not been thoroughly investigated. The objective of this study was to estimate general and specific combining ability effects for pith cell death through a diallel mating design. All possible crosses among six inbred lines (C103, Mol7, B14A, W64A, WIg, and B37) were evaluated at two locations and analyzed according to Griffing's method 2, model 1 (fixed effects for genotypes). General combining ability effects were found to be more important than specific combining ability effects. Heritability of F1 hybrid means was estimated to be 86%. A cyclic selection program might be effective in reducing pith cell death. A reduction in pith cell death would result in stalk-rot resistance which is positively correlated to the presence of living cells in the stalk.
INTRODUCTION
Improving stalk quality in maize (Zea m a y s L. ) has been a continuing challenge to maize breeders as stalk lodging continues to be a major production problem. Stalk rot and associated stalk lodging result in yield losses of 5-25% annually (Zuber, 1973; Zuber and Kang, 1978), Various techniques have been developed to identify and select maize genotypes with superior stalk quality ( Cloninger et al., 1970). A stalk-crushing method described by Zuber and GroNote: Approved for publication by the Director of the Louisiana Agricultural Experiment Station as manuscript number 87-09-1193. Please address reprint requests to Dr. Kang.
0378-4290/87/$03.50
© 1987 Elsevier Science Publishers B.V.
156
gan (1961) has been successfully used to improve stalk quality through several cycles of recurrent selection (Zuber, 1973). Inheritance and procedures for improvement of three important stalk-quality traits, viz., crushing strength, weight of stalk section, and rind thickness, have been reported by several researchers (Loesch et al., 1963; Singh et ah, 1969; Loesch, 1972; Zuber, 1973; Zuber and Kang, 1978; Kang et al., 1979 ). Effects of selection for high and low stalk-crushing strength in two maize synthetics on anatomical features of stalks (Berzonsky et al., 1986) and on agronomic characteristics (Zuber, 1973; Colbert et al., 1984; Berzonsky and Hawk, 1986) have been studied. In addition to the three stalk-quality traits mentioned above, pith (parenchyma) cell death in stalk internodes has been implicated as an important stalk-quality trait (BeMiller and Pappelis, 1965; Pappelis and Williams, 1966; Pappelis et ah, 1971; Kang et al., 1974; Kang et al., 1986). Pappelis ( 1957 ) discoveredthat stalk rot incited by Diplodia maydis (Berk.) Sacc. was related to the death of parenchyma cells in the stalk, and stalk rot resistance was related to the presence of living cells in that tissue. The relationship of pith condition to the spread of stalk-rotting fungi has been studied by several researchers (Craig and Hooker,,1961; Pappelis and Smith, 1963; Pappelis and Williams, 1966; Wysong and Hooker, 1966; Gates, 1970; Pappelis, 1970; Pappelis et al., 1971; Kang et ah, 1974). A highly significant positive correlation between pith cell death and stalk rot ratings was reported by Pappelis and Williams {1966). A decrease in soluble solids in stalks is associated with an increase in stalk lodging due to higher pith cell death and stalk rot ( Craig and Hooker, 1961 ). Pappelis and Katsanos (1969) reported that ear removal resulted in delayed cell death in stalk internodes. Kang et al. {1974) inoculated the cob and shank with D. maydis about 10 days after silking and demonstrated that these inoculations delayed cell death in stalk internodes. Later, Dodd (1977, 1980) proposed the photosynthetic stress-translocation balance hypothesis of predisposition of maize to stalk rot, i.e., any factor that affected ear (sink size) or translocation efficiency would be implicated in stalk rot. However, Schneider and Pendery (1983) have questioned Dodd's hypothesis on the basis that Dodd reported no determinations of stalk condition, rates of photosynthesis or translocation, pith density, water relations or other stress-related physiological processes. Schneider and Pendery (1983) suggested that stress factors that might act as a predisposing agent must be studied separately before a unifying concept can be developed. The relative contributions of rind and pith to total stalk strength are approximately 60 and 40%, respectively (Zuber and Kang, 1978). Pith cell death was found to be negatively correlated with crushing strength and rind thickness of 5-cm-long sections from the second stalk internode (Miller and Myers, 1974). However, inheritance of pith cell death has not been thoroughly investigated. A study involving reciprocal chromosomal interchanges (M.S. Kang, 1987, unpublished data from two locations) indicated that gene loci condition-
157 ing pith cell death in stalk internodes of maize might be many in number and located on several different chromosomes. However, no quantitative genetic study of this trait has been made. The objective of this study was to estimate general and specific combining ability effects for pith cell death through a diallel mating design. MATERIALS AND METHODS
Six inbred lines of maize (C103 and Mo17, low cell death; B14A, W64A and Wf9, intermediate cell death; and B37, high cell death) were crossed in all possible combinations. The resulting 15 F1 hybrids or single crosses were selfed to obtain F2 populations. The parents, F1 hybrids, and F2 populations were planted at the Agronomy Research Farm, Southern Illinois University at Carbondale, Ill., and the Rollins Bottom Maize Nursery, University of Missouri at Columbia, Mo., on June 1 and May 27, 1971, respectively. At each location, a randomized complete block design with three replications was used. The inbreds and F~ hybrids were planted in single-row plots of 5 m length, with 13 plants per row. The rows were spaced 96.5 cm apart, and the plant-to-plant spacing within row was 33 cm. The F2 populations were grown in similar tworow plots. Mid-silking dates for all plots were recorded. Stalks from 13 plants of inbreds and F~ hybrids, and 26 plants of F2 populations were split longitudinally, one day after their respective mid-silking dates. Five consecutive elongated internodes above the brace roots were visually evaluated for pith cell death using the following rating scale developed by Pappelis (1957): 0.0, no white tissue (dead cells) in the pith; 0.1, less than 1% white; 0.5, 2-12% white; 1.0, 13-25% white; 2.0, 26-50% white; 3.0, 51-75% white; 4.0, 76-100% white; 5.0, same as 4.0 with white tissue in the node linking adjacent internodes; and 6.0, same as 5.0 but plant dead. Plot means (mean rating of five internodes per plant over all plants in a plot) were used to estimate general combining ability (GCA) and specific combining ability (SCA) components according to Griffing's (1956) method 2, model 1 (genotypes being fixed effect). Locations were regarded as random effect. The least significant difference (LSD) values were used to test differences among means of inbreds, F1 hybrids, F2 populations, line means (F~), and estimated GCA effects ($i). Mid-parent values for the 15 F~ hybrids were calculated and a rank-correlation coefficient between F1 mean ratings and the mid-parent values was determined. Heritability (broad-sense) among F1 hybrid means was estimated as follows: H = a~l 2 2 2 / ( a~l + a21 × LJl + aeJrZ) where H = heritability (broad-sense), a~l = F1 variance component, aF,2× L / 1 = F~ by location interaction component, a2/rl = error variance component, l= no. of locations, and r = no. of replications.
158
TABLE 1 Combined analysis of variance for pith cell death ratings from Carbondale, Illinois, and Columbia, Missouri Source of variation
(if
Mean square
Locations (L) Replications: L Genotypes (G) Inbreds (I) Single crosses (F1)
1 4 35 5 14 5 9 14 2 35 5 14 5 9 14 2 140
2.494 0.588** 0.885** 1.678"* 0.517"* 1.245"* 0.112 0.769** 2.292 0.O82 O.O94 0.073 0.075 O.O72 0.032 0.066 0.054
GCA SCA F2 populations (F2)
Generations (Gen) L× G L× I L × F1 L × GCA L X SCA L × F2 L X Gen
Pooled error
**Significant at the 1% level of probability. RESULTS AND DISCUSSION
A combined analysis of variance for pith cell death is shown in Table 1. Mean squares for inbreds, FI hybrids, F2 populations, and GCA effects were significant. Replications-within-location effect also was significant. The remainder of effects were not significant at the 5% level. The GCA effects accounted for 86% of the corrected sum of squares among F1 hybrids and the other 14% were attributable to SCA effects, indicating that the GCA effects were much more important that the SCA effects in the six inbreds studied. A study by Arnold and Josephson (1975) of percentage of senescent (dead) stalks also indicated that additive genetic effects were more important than non-additive genetic effects. However, their study did not consider the amount of dead cells in each stalk. Mean cell death ratings for the parental inbred lines~ F1 hybrids, and F2 populations are given in Table 2. Mid-parent values ( M P ) , line means (F1), and estimates of GCA effects for the inbred lines are also shown in Table 2. Mean pith cell death of C103, Mo17, and B14A was significantly lower than that of W64A, Wf9, and B37. Mo17 × C103, a single cross involving two inbred lines with low pith cell death, had the lowest pith cell death of all the FI hybrids. Wf9 × B37 had the
159 TABLE 2 Mean pith cell death ratings of F1 hybrids {abovediagonal ), inbreds (diagonal), F2 populations (below diagonal), mid-parent value (in parenthesis, above diagonal), line means of F~ hybrids ( i~ ) and of mid-parent values (MP), and GCA effects of parental lines C103 Mol7
B 1 4 A W 6 4 A Wi0
B37
F1
MP
GCA effect (gi)
C103
1.53 1.56
B14A
1.37
2.12
2.06 (1.63) 2.23 (1.65) 1.72
W64A 2.28
2.35
2.37
2.47 (1.90) 2.24 (1.93) 2.58 (2.00) 2.27
Wf9
2.07
2.23
2.24
2.48
2.46 (1.92) 2.49 (1.95) 2.61 (2.02) 2.64 (2.29) 2.31
B37
2.10
2.23
2.37
2.65
2.75
2.15 (2.21) 2.47 (2.23) 2.70 (2.30) 2.65 (2.58) 2.98 (2.60) 2.88
2.19 1.84 -0.31
Mo17
1.82 (1.56) 1.58
2.25 1.86 -0.23 2.44 1.92
0.00
2.52 2.14
0.10
2.64 2.16
0.25
2.59 2.38
0.19
Overall means: F1 hybrids = 2.44; F2 populations = 2.21; Inbreds = 2.04. LSD~o.os) for testing differences among. F~ hybrids=0.31; F2 populations=0.33; Inbreds=0.35; F1 - F2= 0.34; i~1= 0.14; ~i= 0.087; ~i-$j = 0.095. highest pith cell death. Ten of the 15 F1 hybrids had higher ratings than the higher pith-cell-death parent, three F1 hybrids were nearly equal to the higher parent, and two were close to their mid:parent values. All the F1 hybrids except C103 X B37 had higher cell-death ratings than their respectivemid-parent values. A rank-correlation coefficient of 0.84 (significant at the 1% level) was found between the cell-death ratings of the F~ hybrids and their corresponding mid-parent values, which suggested that mid-parent values could serve as a reasonable predictor of F1 hybrid cell-death ratings. Four of the six mean midparent values and line means had the same rank, indicating that the M P might be useful in predicting line means or single-cross performance. However, the estimates of GCA effects of the six inbred lines were in the same rank order as the line means, indicating that the use of GCA effects would be better in predicting cell death ratings of F~ hybrids than would mid-parent values. Furthermore, Baker (1978) pointed out that the performance o f a single-cross progeny can be adequately predicted on the basis of general combining ability when specific combining ability mean square is not significant. Gilbert (1958) also indicated that main effects estimated by diallel analysis gave a better prediction than did a regression on mid-parent, taking into account the fact that general combining ability is measured with greater precision than is mid-parent value. The GCA effects of C 103 and Mo17 were negative; of B14A negligible; and of Wf9, B37, and W64A, positive. The use of C103 and Mo17 in breeding pro-
160 grams might be effective in reducing pith cell death and possibly stalk rot and associated stalk lodging. Heritability of F1 hybrid means was estimated to be 86%. The magnitude of GCA effects relative to SCA effects suggested t h a t broadsense heritability of pith cell death would approximate narrow-sense heritability and was mainly due to additive genetic effects. These results, although limited in scope because of the small number of parents involved, indicated that a cyclic selection program might be effective in reducing the a m o u n t of cell death in stalks of maize, thus improving stalk strength. Among individual F1 and F2 comparisons, F2 means were lower than F~ means in all cases except Mo17 × W64A. In three cases, i.e., C103 × B14A, C103 × Wfg, and B 14A × Wf9, the F2 means were significantly lower t h a n the corresponding F1 means, indicating an inbreeding depression characteristic of non-additive gene action. However, the parental lines of the remaining 11 single crosses contributed mainly additive genetic effects as their F2 means were not significantly different from their F1 means. Since pith cell death and spread of stalk-rotting fungi are closely related (Pappelis et al., 1971) and because pith contributes to total stalk strength (Zuber and Kang, 1978), a reduction in pith cell death might cause a corresponding reduction in incidence of stalk rot. Cell death in stalk internodes is measured with ease in the field, The rating system used in the evaluation of pith cell death has been shown to be reasonably precise (Pappelis and Williams, 1966; Pappelis and Katsanos, 1969). Desirable lines may be identified in the field on the basis of a sample of about five plants of inbreds or single crosses. Such identification is possible prior to flowering, thus making it possible to cross the desired lines in the same generation. Selection for low pith cell death could result in stalk-rot resistant plants, as living, hydrated pith cells characterize stalks resistant to Diplodia maydis stalk rot.
REFERENCES Arnold, J.M. and Josephson, L.M., 1975. Inheritance of stalk-quality characteristics in maize. Crop Sci., 15: 338-340. Baker, R.J., 1978. Issues in diallelanalysis. Crop Sci., 18: 533-536. BeMiller, J.N. and Pappelis, A.J., 1965.2-4-Dihydroxy-7-methoxy-1,4-benzoxazin-3-oneglycoside in corn. I. Relation of water-soluble 1-butanol-solubleglucosidefraction content of pith cores and stalk rot resistance. Phytopathology,55: 1237-1240. Berzonsky, W.A. and Hawk, J.A., 1986. Agronomicfeatures of two maize synthetics selected for high and low stalk-crushing strength. Crop Sci., 26: 871-875. Berzonsky,W.A.,Hawk,J.A. and Pizzolato,T.D., 1986. Anatomicalcharacteristicsof three inbred lines and two maize synthetics recurrently selected for high and low stalk-crushing strength. Crop Sci,, 26: 482-488. Cloninger, F.D., Zuber, M.S., Calvert, O.H. and Loesch, P.J., Jr., 1970. Methods of evaluating stalk quality in corn. Phytopathology,60: 295-300.
161 Colbert, T.R., Darrah, L.L. and Zuber, M.S., 1984. Effect of recurrent selection for stalk-crushing strength on agronomic characteristics and soluble solids in maize. Crop Sci., 24: 473-478. Craig, J. and Hooker, A.L., 1961. Relation of sugar trends and pith density to Diplodia stalk rot in corn. Phytopathology, 51: 376-382. Dodd, J.L., 1977. A photosynthetic stress-translocation balance concept of corn stalk rot. Proc. Annu. Corn Sorghum Res. Conf., 32: 122-130. Dodd, J.L., 1980. Grain sink size and predisposition ofZea mays to stalk rot. Phytopathology, 70: 534-535. Gates, L.F., 1970. Relationships between pith cell death conditions as assessed by tetrazolium chloride and incidence of GibbereUa stalk rot in corn. Can. J. Plant Sci., 50: 674-684. Gilbert, N.E.G., 1958. Diallel cross in plant breeding. Heredity, 12: 477-494. Griffing, B., 1956. Concept of general and specific combining ability in relation to diallel crossing systems. Aust. J. Biol. Sci., 9: 463-493. Kang, M.S., Pappelis, A.J., Mumford, P., Murphy, J.A. and BeMiller, J.N., 1974. Effect of cob and shank inoculations (Diplodia maydis) on cell death in stalk internodes of corn. Plant Dis. Rep., 58: 1113-1117. Kang, M.S., Zuber, M.S., Myers, O. and Colbert, T.R., 1979. Genetic studies on three stalk traits in maize using chromosomal interchanges. Can. J. Genet. Cytol., 21: 139-144. Kang, M.S., Pappelis, A.J. and Zuber, M.S., 1986. Effect of stalk inoculation (Diplodia maydis) on parenchyma cell death in cob and shank internodes of maize. Cereal Res. Commun., 14: 267-272. Loesch, P.J., Jr., 1972. Diallel analysis of stalk quality traits in 12 inbred lines of maize. Crop Sci., 12: 261-264. Loesch, P.J., Jr., Zuber, M.S. and Grogan, C.O., 1963. Inheritance of crushing strength and rind thickness in several inbred lines of corn. Crop Sci., 3: 173-174. Miller, T.L. and Myers, O., 1974. Correlation of pith cell death with various stalk quality characteristics in two synthetic populations of maize. Crop Sci., 14: 215-217. Pappelis, A.J., 1957. Nature of resistance to Diplodia stalk rot of corn. Ph.D. Thesis, Iowa State University, Ames, Ia., 204 pp. Pappelis, A.J., 1970. Effect of root and leaf injury on cell death and stalk rot susceptibility in corn. Phytopathology, 60: 355-357. Pappelis, A.J. and Katsanos, R.A., 1969. Ear removal and cell death rate in stalk tissue. Phytopathology, 59: 129-131. Pappelis, A.J. and Smith, F.G., 1963. Relationship of water content and living cells to spread of D iplodia zeae in corn stalks. Phytopathology, 53: 1100 - 1105. Pappelis, A.J. and Williams, J.R., 1966. Patterns of cell death in the elongating corn stalks. Trans. Ill. State Acad. Sci., 59: 195-198. Pappelis, A.J., BeMiller, J.N., Schmid, W.E., Myers, O. and Murphy, J.A., 1971. Stalk rot of corn. Proc. Annu. Corn Sorghum Res. Conf., 28: 110-122. Singh, T.P., Zuber, M.S. and Krause, G.F., 1969. Relationship of certain stalk characters with grain yield in corn (Zea mays L. ). Crop Sci., 9: 265-267. Schneider, R.W. and Pendery, W.E., 1983. Stalk xot of corn: mechanism of predisposition by an early-season water stress. Phytopathology, 73: 863-871. Wysong, D.S. and Hooker, A.L., 1966. Relation of soluble solids content and pith condition to Diplodia stalk rot in corn hybrids. Phytopathology, 56: 26-35. Zuber, M.S., 1973. Evaluation of progress in selection for stalk quality. Proc. Annu. Corn Sorghum Res. Conf., 28: 110-122. Zuber, M.S. and Grogan, C.O., 1961. A new technique for measuring stalk strength in corn. Crop Sci., 1: 378-380. Zuber, M.S. and Kang, M.S., 1978. Corn lodging slowed by sturdier stalks. Crop Soils, 30 (5)N: 13-15.