| Efficacy of single crosses versus three-way hybrids
in tetraploid Triticum species S.N. TALWAR and M.G. JOSHI Department of Agricultural Botany, college of Agriculture, Dharwad-5, Karnataka State, India. and Division of Genetics, IARI, New Delhi-110012. Improvement of yield in wheat through conventional breeding methods has reached a level at which phenomenal increase seems to be rather difficult (SINGH & SINGH 1971). One of the important breeding approach for bringing about further genetic upgrading in any crop plants is through the utilization of useful genetic resources from allied species (HAWKES 1977). Tetraploid Triticum (emmer) group includes species and subspecies known for some important agronomic features, that help in building up various yield components and ultimately the yield. This sort of component breeding approach has also been suggsted by WILLIAMS (1959,1960), GRAFIUS (1959) and MOLL et al. (1962). In case of interspecific hybridization, once the desirable genes from allied species are incorporated, it is necessary to recover the proper agronomic base. This is achieved through three-way cross involving third parent as well adapted one. Such an approach has potential advantages over single crosses by way of creating a genetically heterogeneous population. This heterogeneity may give an opportunity for transgressive segregation,better recombinants and some degree of populational buffering (WALSH & ATKINS 1973). The present study deals with the magnitude of heterosis in single and three-way cross hybrids and also assesses the extent of improvement of three-way hybrids over single cross. Heterosis studies involving emmer species is very limited. Materials and methods A line x tester design involving five tetraploid Triticum species and four durum cultivars were used as parents to get 20 F1 hybrids. Part of the seeds from all 20 single crosses were grown at Wheat Breeding Regional Research Station, Wellington (Nilgiris) during summer for attempting three-way crosses with an adapted variety JNK-4w-184 as a pollinator. The five tetraploid Triticum species viz., T. dicoccum var. NP. 202 (A), T. polonicum var. Polish (B), T. carthlicum-39584 (C), T. turgidum-45(D) and T. pyramidale var. Sendioni (E) were selected on the basis of their diversity of origin and widely different yield components. Similarly five durum types namely, A206(F), Raj911(G), NP404(H), Sel. 389 (I) and JNK-4w-184 (J) are under cultivation in different zones of India. The alphabets in parenthesis will be used while referring the cross combinations. The experiment consisted of 10 parents, 20 each of single cross (SC) and three-way cross (TWC) populations. The layout was randomised block design with three replications. Out of 120 rows in each replicate, 4 rows were sown to each parent, 2 rows to each SC and TWC. The sowing was done by dibbling the seed at a distance of 30 cm rows in 3 meter long, spaced 15 cm apart. Ten random plants were selected and following observations were recorded viz.; ear weight, 1000-grain weight, grains per ear, flag leaf size and grain yield per plant. Analysis of variance was done on the data for each of the five characters. Heterosis was determined as percentage increase or decrease in SC and TWC hybrids over their corresponding mid parent and better parent. The heterosis in three-way hybrids was computed like F1, but the mean of mid parent (MP) in this case of F+P3/2 (where, P3=mean of third parent involved in the cross). The 't' tests were done to determine whether the F1 and three-way cross hybrid value differed significantly from the value of mid or better parent. |
| Part of a thesis submitted by the senior author in partial fulfillment of the requirements for the Ph. D. degree at Indian Agricultural Research Institute, New Delhi. |
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