Environmental Physiology of Sorghum. I. Environmental and Genetic Control of Epicuticular Wax Load1

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Abstract
The effects of genotype and environment on the epicuticular wax (EW) load on sorghum [Sorghum bicolor (L.) Moench.] leaves were studied in a series of field experiments between 1976 and 1981. Entries in the tests were normal, bloom‐type sorghums and represented a range of lines and hybrids. Leaf samples were collected near anthesis, EW was extracted with chloroform, and quantities of EW were estimated by a colorimetric method. In a 4‐year test at Temple, Tex., significant variability in average EW loads occurred among genotypes (0.97 to 1.63 mg dm−2) and among years (0.91 to 1.51 mg dm−2). EW loads increased under hot, dry conditions, but wax loads were not closely related to seasonal rainfall. General and specific combining abilities were determined in a study of 30 F1 hybrids from crosses between six male and five female parents in five environments. General combining abilities of both males and females were significant (P < 0.001), but specific combining ability effects were not significant. Both the broad and narrow‐sense heritabilities were estimated at 36.0%. Because the parents were not chosen in a random manner, these estimates only pertain to our specific germplasm and cannot be considered general. The portion of the genetic variance contributed by females was 73% while the males contributed 27%. The best parental lines for increasing EW loads in hybrids were RTx430 among the males and ATx623 among the females. RTx7078, RTx7000, and A4R generally decreased the EW load of their hybrids. Genetic stability for EW load across environments also varied. The value of low genetic stability of adaptive responses such as EW loads for crops grown in drought‐prone environments is discussed.