Abstract
The effect known as depression by inbreeding refers to the reduction on the average value of quantitative traits, related to plant reproduction and physiology, due to the homozygosis of deleterious alleles. This study evaluated the inbreeding depression and the genetic variability of agricultural traits and of the resistance to phytopathogens in inbred families of two exotic maize populations. The experiments were done in the experimental area of the Universidade Federal de Goiás, Regional Jataí, in the second harvest 2015. Fifty and 40 FS1 of NAP5 and NAP7 populations, respectively, were evaluated interplanting one row with a mixture of base population at every ten plots to estimate depression by inbreeding of the traits evaluated. The experimental design was randomized blocks, with three replications. The following traits were evaluated: AP – plant height (cm), AE – ear height (cm), FM – male flowering (days), PQ – number of broken plants, AC – number of lodged plants, PG – kernel production (kg plot-1). The greatest estimates of depression by inbreeding in the agricultural traits were observed for kernel production, with values of 51.2 and 38.9% for the populations NAP5 and NAP7, respectively. Among the traits of resistance to phytopathogens, the greatest estimate was observed for the stunting complex, with values of -58.9% in NAP5 and -74.2% in NAP7. Both populations under study presented genetic potential to be used in breeding programs with recurrent selection and, after some selection cycles, lineages with good agricultural standard and resistance to phytopathogens can be obtained.
Highlights
Endogamy is defined as a phenomenon that occurs due to mating between related individuals (CRUZ, 2005)
Oftentimes endogamy is undesirable in Hardy-Weinberg equilibrium populations, such as maize, because this type of crossing leads to homozygosis and, in these populations, there are recessive deleterious genes that, in homozygosis, cause harm to plant physiology, decreasing its phenotypic value (MIRANDA FILHO, 2001)
This study evaluated inbreeding depression and the genetic potential of agricultural traits and the resistance against plant pathogens (Exserohilum turcicum Leonard and Suggs, Pantoea ananatis (White Spot), phytoplasm, spiroplasm, Puccinia polysora and (Cercospora Leaf Blight) Cercospora zeae Tehon and Daniels) in endogamic families of two exotic maize populations
Summary
Endogamy is defined as a phenomenon that occurs due to mating between related individuals (CRUZ, 2005). The genetic causes controlling inbreeding depression are not completely known; there are some hypotheses to explain them One of these hypotheses is that favorable genes tend to be dominant or partially dominant; another hypothesis states that the heterozygote has greater phenotypic value than the homozygote (CROW; KIMURA, 1970). Inbreeding depression, in the former, is the rupture of the ideal combination of alleles that control the character under study. Self-fertilization is the driving mechanism of endogamy, since it allows that common alleles by ancestry be found in the same individual, presenting great importance to obtain lineages. In order to obtain lineages with acceptable probability, a breeding program should start with populations with high frequency of favorable alleles of important
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