Drought is considered a major threat to rice production. This study aimed to determine the effects of drought stress on the estimates of heterosis and the combining ability of rice genotypes for the number of days to 50% heading, plant height, number of panicles per plant, panicle length, number of filled grains per panicle, and grain yield per plant. Field experiments were conducted at the Rice Research and Training Center, Kafr El Sheikh, Egypt, during the rice-growing season in 2018 and 2019. Eight rice genotypes (Giza178, Giza179, Sakha106, Sakha107, Sakha108, WAB1573, NERICA4, and IET1444) were crossed in a half-diallel cross in the rice-growing season in 2018, which yielded a wide range of variability in numerous agronomic traits and drought tolerance measurements. In 2019, these parents and their 28 F1 crosses were produced by employing a three-replication randomized complete block design under normal and water stress conditions. The results showed remarkable differences across the studied genotypes under normal and water stress conditions. Under both conditions, Sakha107 was the best general combiner for earliness and short stature. Giza179 and Sakha108 were the best general combiners for grain yield per plant and one or more of its characteristics. Furthermore, in both normal and water stress conditions, Giza179 exhibited the highest general combining ability effects for all attributes that were evaluated. Under normal and water stress conditions, the Giza179 × Sakha107 cross demonstrated substantial and desirable specific combining ability effects on all the examined traits, which suggested that it could be considered for use in rice hybrid breeding programs. Therefore, we recommend that these vital indirect selection criteria to be considered for improving rice grain yield under drought conditions.
This research was carried out at the Experimental Farm, Faculty of Agric., Kafr El-Sheikh Univ. The aim of the experiment was to study heterosis and combining ability for the most important traits of maize (Tasselling and silking dates, plant and ear heights, ear length, ear diameter, number of rows/ear, number of kernels/row, 100 grain weight and grain yield (ardab/fed.) Seven inbred lines of corn were crossed in one half diallel cross in 2004. The resulted 21 single crosses in addition to three recommended commercial crosses, were grown in a randomized complete block design in 2005 season. The variation among single crosses were partitioned into gca and sca, using griffing's method 4 model 1. The results are summarized as follows: 1.Highly significant differences were found among the studied inbred lines, also the gca effects were significant for all studied traits and the sca effects also, were, significant, except for 100-grain weight. 2.The cross (P5 x P6) was the earliest for tasseling and silking dates. The crosses (P3 x P7) and (P5 x P7) were of desirable performance for plant and ear heights. Mean while the cross (P1 x P2) was the best cross for ear length and number of kernels per row and grain yield/fed. and cross (P4 x P6) for ear diameter and number of rows/ear and the single cross (P1 x P4) for 100-grain weight. 3.The gca/sca ratio revealed that importance of additive genetic variance in the inheritance of all studied traits, except plant height and number of rows/ear. 4.The best general combining ability for earliness were lines P3, P4, P5, P6 and P7, while for grain yield ardab/fed. were lines P1, P2 and P3. 5.Estimate of specific combining ability effects indicated that the best crosses were 3 x 4 for tasseling date, silking date and ear height, the cross P2 x P7 for plant height, the crosses P3 x P6, P4 x P7, P4 x P6, P6 x P7 and (P1 x P3) for ear length, ear diameter, number of rows per ear, number of kernels per row and weight and 100-kernels, respectively, while the cross (1 x 2) showed the best desirable sca effects for grain yield ard./fed. 6.The cross (P 5 x P6) showed negative and significant useful heterosis for tasseling and silking dates relative to the earlier check, while the crosses (P3 x P7) and (P5 x P7) had negative and significant useful heterosis relative to the shortest check for plant and ear heights, respectively. The cross (P1 x P2) for ear length and number of kernels per row, (P4 x P6) for ear diameter and number of rows per ear, (P1 x P4) for weight of 100 kernels, and (P1 x P2) for grain yield ardab/fed. showed positive and significant heterosis relative to superior check in these traits. 7.The best cross (P1 x P2) was the superior one which significantly outyielded the three checks.
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