Genetic variance and covariance components related to intra- and interpopulation recurrent selection in maize (Zea mays L.)

Abstract

New genetic variance and covariance components related to intra- and interpopulational recurrent selection methods have been theoretically developed by Souza Jr. (Rev. Bras. Genet. 16: 91-105, 1993) to explain the failure of these methods to concomitantly develop hybrid and per se populations. Intra- and interpopulation half-sib progenies of 100 genotypes were sampled from maize (Zea mays L.) populations BR-106 and BR-105 to estimate variance and covariance components and to compare the expected responses to reciprocal (RRS), intrapopulational (HSS), and modified (MRS) recurrent selection in interpopulation hybrid, populations per se, and to determine heterosis. Four sets of 100 progenies, two intra- and two interpopulational, were evaluated in partially balanced 10 x 10 lattices arranged in split-blocks with two replications in two years (1991/92 and 1992/93) and two locations in Piracicaba, SP. Data for ear weight, plant and ear height, and ear by plant height ratio were recorded. Populations and interpopulation crosses were high yielding and showed high breeding potential for production of hybrids from inbred lines. Mid parent and the highest parent heterosis were relatively high, but lower than values reported for these populations under other environmental conditions. Additive variance estimates of populations per se and interpopulation crosses confirmed the high potential of these materials. The magnitude of the variance estimates for the deviations from intra- and interpopulation additive effects (<img src="http:/img/fbpe/gmb/v21n4/1918f1.jpg" alt="1918f1.jpg (1262 bytes)" align="middle"> for BR-106 and <img src="http:/img/fbpe/gmb/v21n4/1918f3.jpg" alt="1918f3.jpg (1259 bytes)" align="middle">for BR-105) and covariance between additive effects with these deviations (<img src="http:/img/fbpe/gmb/v21n4/1918f2.jpg" alt="1918f2.jpg (2022 bytes)" align="middle"> for BR-106 and <img src="http:/img/fbpe/gmb/v21n4/1918f4.jpg" alt="1918f4.jpg (1995 bytes)" align="middle"> for BR-105) indicated that these new components can significantly influence the effectiveness of breeding methods. Genetic component estimates for BR-105 had relatively small errors, with <img src="http:/img/fbpe/gmb/v21n4/1918f4.jpg" alt="1918f4.jpg (1995 bytes)" align="middle"> negative for all traits. Estimates of <img src="http:/img/fbpe/gmb/v21n4/1918f1.jpg" alt="1918f1.jpg (1262 bytes)" align="middle">and <img src="http:/img/fbpe/gmb/v21n4/1918f2.jpg" alt="1918f2.jpg (2022 bytes)" align="middle"> had relatively larger errors for BR-106. The MRS method was more effective than the RRS and HSS methods in producing hybrids from inbred lines. The choice of a population tester for the MRS method based on population means per se may be incorrect. The additional use, when possible, of intra- and interpopulation additive genetic variances from each population would be more appropriate.

Estimates for Genetic Variance Components in Reciprocal Recurrent Selection in Populations Derived from Maize Single-Cross Hybrids

“…These estimates were obtained using the procedure of iterative weighted least squares β = ( X ′ V −1 X ) −1 X ′ V −1 Y and the standard error came from the square root of diagonal matrix ( X ′ V −1 X ) −1 , similar to the procedure presented by Arias and Júnior [19]. …”

Genetic Parameters and Predictive Genetic Gain in Maize with Modified Recurrent Selection Method

“…There was reduction of about 50% in the for PH and EH from first cycle to second cycle of selection. These for EH and PH in second cycle were smaller than those found by Arias and Souza Jr. (1998) The additive genetic variance estimates ( and ) of EW in the first cycle were similar between the intra and inter population progenies (Table 4). Arias and Souza Jr. (1998) found an of 376 (g plant -1 ) 2 and an of 281 (g plant -1 ) 2 for the BR 106 dent population and an of 442 (g plant -1 ) 2 and of 522 (g plant -1 ) 2 for the BR 105 flint population.…”

“…The magnitudes of were five and eight times larger in the first than the second cycle for PH and EH, respectively, and both the signs were positive (Table 4). The estimates obtained by Arias and Souza Jr. (1998) The values of Côv(A 1τ12) were negative for all traits ( Table 4). Note that the PH and EH covariance for the first cycle had the same sign but different magnitudes.…”

“…These were used to estimate the intra-population additive genetic variance of the SynFlint population ( ), the inter-population additive genetic variance ( ), the additive genetic covariance between types of progenies [Cov(A 1A12) ], the genetic variance of the deviations from inter-population and intra-population additive effects of the SynDent and SynFlint populations ( ), and the genetic covariance of the intra-population additive effects with the deviations from the inter-population and intrapopulation additive effects of the SynDent and SynFlint populations [Cov(A 1 τ 12) ]. These new variance and covariance components were estimated using a procedure similar to that presented by Arias and Souza Jr. (1998) Parametersî nter progenies were significant for all traits in the first cycle of selection and for PH and EH in the second cycle of selection. These results showed that genetic variation among progenies was detected, which can be related to their heterosis, and thus the possibility of obtain of the hybrids highly yield of the lines derived from populations (Hallauer et al, 2010).…”

“…Therefore, this author proposed a new modified recurrent selection method using a population with a low yield (B) to evaluate another population with superior performance (A) and itself (B), leading to an average increase in the two populations per se and also in heterosis because population A increases the combining ability with population B. Therefore, the increase in heterosis occurs to a lesser extent than in traditional reciprocal recurrent selection, but the two populations will be improved with adequate genetic gains (Arias and Souza Jr., 1998). As the increase in the average inter-population hybrid is a function of improved populations per se and heterosis, the modified recurrent selection method is thought to be as efficient as selection in the traditional reciprocal recurrent method.…”