Intergenotypic Competition Between Tall and Dwarf Wheats. II. In Hybrid Bulks¹

Abstract

Intergenotypic competition was studied in populations developed from a hybrid of two wheats (Triticum aestivum L. em. Thell.), ‘D6301’ (short‐statured) and ‘Ramona 50’ (standard‐height). The F2 through F6 generations were grown in the field in two replicate subpopulations without artificial selection. Heights of individual plants, taken from the F3, F4, F5, and F6 bulk populations, were studied in the same environment. Mean height increased and frequency of short‐statured plants decreased markedly from F3 to F6. Height of 62 random lines isolated from each of the F2, F4, and F6 generations showed a decrease in phenotypic variance from F2 to F6. Grain yields of the F2, F4, and F6 bulk populations and the means of 62 random lines (in F3, F5, and F7) indicated a significant increase from the F4 to F6 and from the F5 to F7 generations. At F7 the yield of the bulk population equalled the yield of the lower‐yielding parent, Ramona 50. Variance in yield among lines increased from F3 to F7, but extremely short genotypes did not appear in the F7. Extremely tall genotypes yielded less than those of intermediate height. Thus, in the bulk population directional and stabilizing selection affected both yield and plant height. Some lines in the F7 had higher yields than either parent. Thus, in spite of natural selection against the agronomically desirable short plants, the bulk populations were useful as source materials in selection for increased grain yield.

Structuring an Efficient Organic Wheat Breeding Program

“…If there were a modification to the above approach, it would be to grow the early generation bulks in an organic production system. Competition within a bulk is well documented [27,28] and it may be that the competition in bulk under organic production practices is different from those under conventional systems. The advantage of this modification is that it can be coupled with on-farm testing (as certified organic testing sites remain rare among universities and private companies) and with participatory plant breeding [26,29].…”

“…Simply a cross between an adapted Nebraska line by an adapted Oklahoma line should produce progeny adapted to Oklahoma, Kansas, and Nebraska (assuming no transgressive segregation, and a wider potential area of adaptation if there were transgressive segregation). However if those progeny and early generation bulks are only grown in Nebraska, the progeny adapted to Oklahoma and Kansas may be quickly lost due to competition within the bulk and selection for excellent winter hardiness, which is less needed in Oklahoma and Kansas [27,28].…”

Functional agrobiodiversity and agroecosystem services in sustainable wheat production. A review

“…This problem is worsened when dealing with bulk populations where intraspecific competition may have an even stronger impact. Competition between tall and dwarf wheat genotypes was studied by reproducing both bulk physical mixtures (Khalifa and Qualset 1974) and bulk hybrid populations (Khalifa and Qualset 1975), showing a competitive advantage of tall genotypes and, in the case of hybrids, a net increase in height across generations, followed by stabilising selection for intermediate height.…”

Statistical Designs and Response Models for Mixtures of Cultivars1

“…The beneficial or detrimental effects of using mixtures as compared to monoculture (solid seeding, sole cropping) needs to be assessed. Various aspects of statistical design and analysis have been considered by many authors under the topics of diallel crossing or competition (e.g., see Hanson et al, 1961;Jensen andFederer, 1964, 1965;Rawlings, 1974;Kawano et al, 1974;Khalifa and Qualset, 1974;Jensen, 1978;Laskey and Wakefield, 1978…”