HETEROSIS AND COMBINING ABILITY FOR YIELD AND ITS COMPONENTS IN SOME CROSSES OF SOYBEAN.

Abstract

The present investigation was carried out at Itai El-Baroud Agricultural Research Station, during the two growing summer seasons,2008and 2009 to study heterosis , combining ability and genetic variance components for several traits in soybean i.e, earliness, growth attributes, yield, yield components , oil and protein content. A half diallel set of crosses using six genotypes of soybean (Glycine max) were used namely; (1) L86-K- 73, (2) Giaza111, (3) Giza22, (4) H88L,(5) H155 and (6) DR101 in the first season.

In the second season, the six parents and their 15 F1 crosses were planted in a randomized complete block design with three replicates. Data recorded on 10 individual plants were chosen at random from each plot. Analysis of variance for each trait was firstly performed and then the combining ability analysis was used according to Griffing (1956) method 2, modlel. Heterosis was estimated as the percentage deviation ofF1 mean from mid-parent and better parent values. The genetic components and heritability estimated for all traits in broad and narrow sense. The obtained results could be summarized as follows.

1- Earliness and growth traits:

1- Highly significant mean squares due to genotypes (parents and their crosses) were detected for earliness traits and growth attributes indicating wide diversity between the parental genotypes ofthis study. 2- The parent L86-K-73 behaved as the earliest one for flowering date, maturity date and maturity period, while parent Giza111 was the best for plant height and parent DR101 the best for number of branches/plant.

3- The F1 cross (L86-K-73xH155) was the earliest one among fifteen crosses; it gave the lowest mean values in flowering date and maturity date.

4- The cross (L86-K-73x H88L1) was the tallest among all crosses, while cross (Giza111xDR101) gave the highest mean value in number of branches/plant.

5- Highly significant negative heterotic effects relative to mid-parent for flowering date was detected for two crosses (L86-K-73xGiza111) and (L86-K-73xH88L1).

6- Concerning maturity period one cross (Giza22xH155) expressed significant negative heterosis relative to mid-parent and better parent.

7- For plant height, six and four crosses exhibited highly significant positive heterotic effects to mid-parent and better parent respectively.

8- For number of branches/plant, eleven and eight crosses showed highly significant positive heterotic effects relative to mid-parent and better parent, respectively.