Date of Award
Doctor of Philosophy
Plant, Soil and Environmental Sciences
R.R. Shrode, G.E. Hunt, V.H. Reich, L.N. Skold, J.W. Hilty
The study involved two soybean (Glycine max L. Merrill) intervarietal hybrids—D54-2437 X D65-3054 and Hill x S-100. D54-2437 and S-100 are early flowering, indeterminate in growth habit and have gray pubescence color, while D65-3054 and Hill flower later, are determinate in growth habit and have tawny pubescence. The F2 generation of the cross D54-2437 x D65-3054 was studied both in 1969 and 1970, while the cross Hill X S-100 was grown only in 1970. The parents and the F1 hybrids were also included with the F2 populations in 1970. The F3 progenies of the cross D54-2437 x D65-3054 were studied in replicated trials at Knoxville and Jackson, Tennessee, in 1970. Correlation and heritability estimates were obtained from the data on each cross and each generation.
Correlations indicated significant positive associations of yield, genotypically and phenotypically, with date of flowering, date of maturity, length of fruiting period, plant height and, to some extent, seed size. Oil content was found to be correlated positively with height and seed size. Protein content was negatively correlated with oil content.
Broad sense heritability estimates were, in general, high in the F2 and F3 generations. Narrow sense estimates ranged from zero (for oil content) to 87 percent (for time of flowering) on a progeny basis. Regression of F3 progenies on F2 plants gave smaller estimates than the above broad sense estimates obtained in the F2 and F3 generations separately.
Mite infestation occurred in 1970 and indicated that the reaction of plants to mite incidence in the cross Hill x S-100 was monogenically controlled while in the cross D54-2437 x D65-3054 susceptibility was due to the complementary epistatic action of 2 pairs of genes, each present in a different parent. The gene symbol (Mtmt) has been proposed for resistance and susceptibility in the two crosses.
The number of genes differentiating the parents in each cross for each character studied varied from 3 to 5 pairs when estimated by Mendelian ratios. No satisfactory estimates were obtained by using the Castle- Wright and Burton formulae.
Predicted genetic advances for yield in different combinations of characters used in selection indices indicated that an index consisting of yield and maturity was more efficient than when selection was based on yield alone. The addition of seed weight and lodging did not improve the efficiency significantly.
Greenhouse tests on hypocotyl color indicated that a single gene controls both hypocotyl and pubescence color in the cross Hill x S-100. Studies pertaining to the mosaic virus disease, which causes leaf and seed-coat mottling, indicated the possibility of isolating genetically resistant types in the cross D54—2437 x D65-3054.
Parameswarappa, Raravi, "Association and heritability studies of oil, protein and agronomic characters in two soybean hybrids. " PhD diss., University of Tennessee, 1971.