Reciprocal crosses between 3‐dwarf and 2‐dwarf lines of grain sorghum differing only at the Dw2 locus were grown in the summer of 1963. The effect of plant height on yield was studied to elucidate mechanisms or causes of superior yields of tall genotypes and to determine if higher yields might be achieved in combine height sorghums. It was concluded from light availability data that the taller 2‐dwarf parent and F1's were perhaps more efficient in utilization of available light due to spatial arrangement of leaves. The data suggested that the yield level of the taller 2‐dwarf line may not be recovered rapidly in the shorter 3‐dwarf line by manipulation of alleles at the Dw2 locus conditioning height.

The World Oat (Avena spp.) Collection (4,533 entries) was evaluated in replicated experiments in 1963‐64 for tolerance to soil‐borne oat mosaic virus, Marmor terrestre var. typicum and M. terrestre var. oculatum McK. In 1964‐65, 601 entries were repeated that scored less than 4 on a 0 to 10 rating (0 = no visual symptoms and 10 = completely susceptible or dead plants). Of these 601 entries, the 37 that scored less than or equal to 2.5 are listed.From this evaluation several excellent divergent sources of tolerance to soil‐borne oat mosaic virus were noted.

Information was obtained on the reaction of segregating populations of oats (Avena byzantina C. Koch and Avena sativa L.) to soil‐borne oat mosaic virus, Marmor terrestre var. typicum. Bulk F3 lines were evaluated at two locations that had natural mosaic infestation in the soil. Frequency distributions of mosaic scores indicated that tolerance to OMV was a quantitative character. Heritability estimates based on progeny means ranging from .59 to .88 indicated that a large portion of the variability in tolerance to the virus is heritable. A heritability estimate based on individual plots was lower. Estimates of expected genetic advance indicated that selection of 5% of the more tolerant lines would result in lower mosaic scores, although the resulting scores would not approach the tolerant parent. Evaluation for tolerance at one location was a reliable indication of tolerance at the second location.

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