Earthworms: the 'unheralded soldiers of mankind' and 'farmer's friend' working day and night under the soil: reviving the dreams of Sir Charles Darwin for promoting sustainable agriculture.

Abstract

2 Abstract: A half-diallel set of crosses was established among six local cotton varieties: Giza-88, Giza 90, Giza 87, Giza 89, Giza 91 and Giza 83 in order to estimate the genetic parameters of seed-cotton yield and its components under two divergent environments of clay-fertile and a sandy-calcareous infertile soils. The average reduction in seed-cotton yield/plant under drought stress were 42 and 37.4% and in lint yield/plant were 46.2 and 40.5% for the parent and it is F hybrids, respectively. The results revealed that the additive and 1 non-additive gene effects were involved in the control of the studied traits in both environments. Most of the variation was attributed to the non-additive gene effects. For seed-cotton yield per plant and boll weight the additive gene effects were more important under favorable conditions but under stress, the non-additive effects of the genes were more important. The Wr/Vr analysis revealed that over-dominance was operating for the F1 generation and partial dominance was detected for the F generation under the two environments. The order 2 of the dominance of the cultivars was reversed under drought. The genetic parameters indicated unequal distribution of dominant and recessive alleles among the six parents analyzed. Narrow-sense heritability values were much smaller relative to broad-sense heritability in the two environments indicating that the additive component was smaller than the other components of variance.