Submitted to: Journal of Cotton Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/30/2002
Publication Date: 3/1/2002
Citation: PERCY, R.G., MOSER, H., HUTMACHER, R., WRITE, S. HERITABILITY OF TOLERANCE TO EARLY FOLIAR DECLINE IN THREE AMERICAN PIMA COTTON POPULATIONS.. JOURNAL OF COTTON SCIENCE 6. 2002. 104-114 Interpretive Summary: Early foliar decline is a recurring problem of Pima cotton in the San Joaquin Valley of California, where it has been implicated in yield and fiber quality losses. Anecdotal evidence indicates that genetic variability for tolerance to early foliar decline exists within Pima germplasm. The primary objectives of the present investigation were to determine the heritability of tolerance and susceptibility to early foliar decline and to identify earlier maturing, early foliar decline tolerant germplasm. Heritability estimates obtained in early generations were low and appeared to preclude efficient selection for early foliar decline tolerance. Greater heritabilities were obtained in progeny of later generations, suggesting the feasibility of selection for tolerance; but the highest heritability estimates occurred among replicated advanced generation tests conducted across locations. A negative association between early foliar decline tolerance and early maturity, observed within populations, may indicate difficulty in simultaneous selection for early foliar decline tolerance and early plant maturity. Moderate gains were made in identifying early foliar decline tolerance within earlier maturing genotypes. Results from this investigation should aid in the breeding and selection for early foliar decline tolerant Pima germplasm by public and private improvement programs.
Technical Abstract: Early foliar decline (EFD) is a recurring problem of Pima cotton (Gossypium barbadense L.) in the San Joaquin Valley of California where it has been implicated in yield and fiber quality losses. Anecdotal evidence indicates that genetic variability for tolerance to EFD exists within Pima germplasm. The primary objectives of the present investigation were to determine the heritability of tolerance and susceptibility to EFD and to identify earlier maturing EFD tolerant germplasm. Three populations (96084, 97016, and 96117) were created by crossing putatively EFD tolerant and susceptible parents. Evaluations for EFD, agronomic traits, and fiber quality were conducted in the F_2, F_3, and F_4 generations of the three populations over three successive years at Tulare and Buttonwillow, CA. EFD heritability estimates between F_2 individual plants and F_3 progeny rows were low (h^2=0.14-0.19), and appear to preclude efficient selection for EFD tolerance in the F_2 generation. Higher F_3:F_4 heritability estimates (h^2=0.37-0.46) suggest that selection may be feasible in unreplicated early generation (F_3) progeny rows. However, the highest heritablity estimates occurred among replicated F_4 progeny rows (h^2=0.84-0.89), indicating that the greatest selection efficiency could be expected in advanced generation tests planted at multiple locations. EFD was negatively correlated with final plant heights of F_3 and F_4 progeny at both Tulare and Buttonwillow, and with nodes above bloom (r= -0.47 to -0.61) of F_4 progeny at Tulare. The negative correlation of EFD ratings with final plant heights and nodes above bloom suggest positive relationships between EFD severity, early plant maturity, and increased determinacy; and may indicate difficulty in simultaneous selection for EFD tolerance and early plant maturity. Moderate gains were made in identifying EFD tolerance within earlier maturing genotypes.