Identification and characterization of maize lines resistant to leaf diseases

Abstract

Among the maize leaf diseases, white leaf spot, northern leaf blight, gray leaf spot, and southern rust are recognized not only by the potential for grain yield reduction but also by the widespread occurrence in the producing regions of Brazil and the world. The aim of this study was to characterize common maize lines for resistance to white leaf spot, northern leaf blight, gray leaf spot, and southern rust and suggest crosses based on the genetic diversity detected in SNP markers. The experiment was conducted in a randomized block design with three replications in order to characterize 72 maize lines. Genotypic values were predicted using the REML/BLUP procedure. These 72 lines were genotyped with SNP markers using the 650K platform (Affymetrix®) for the assessment of the genetic diversity. Genetic diversity was quantified using the Tocher and UPGMA methods. The existence of genetic variability for disease resistance was detected among maize lines, which made possible to classify them into three large groups (I, II, and III). The maize lines CD 49 and CD50 showed a good performance and can be considered sources of resistance to diseases. Therefore, their use as gene donors in maize breeding programs is recommended. Considering the information of genetic distance together with high heritability for leaf diseases, backcrossing of parent genotypes with different resistance levels, such as those of the lines CD49 x CD69 and CD50 x CD16, may result in new gene combinations, as they are divergent and meet good performances.

Mixed Modeling in Genetic Divergence Study of Elite Popcorn Hybrids (Zea mays var. everta)

“…In more recent years, mixed models have been increasingly employed in breeding programs involving annual crops since the robustness of this methodology had already been demonstrated in many perennial species regarding the estimates of genetic parameters [36][37][38]. Some examples of studies involving annual crops include soybean [39], common maize [40,41], and popcorn [1,42,43]. Given the potentiality of the statistical technique and the demand for reliable superior popcorn genotypes to be used in the seed industry, the REML/BLUP methodology was used to examine the genetic divergence among six controls and forty diallel hybrids and to indicate traits associated with greater resistance of these genotypes to diseases caused by E. turcicum and B. maydis, which have a great impact on the reduction in yield in popcorn culture.…”

“…This cut-off point proved to be efficient to evaluate the phenotypic association among landraces and to determine clusters of popcorn genotypes in a work developed by Cheim et al [44]. Studies on diversity in the genus Zea based on morpho-agronomic variables have been successfully performed to form clusters based on the UPGMA methodology [41,[45][46][47][48]. The cophenetic correlation coefficient of 0.70 demonstrated a good consistency of the clustering pattern, and it is such to estimate a linear correlation between the distance matrix elements and the elements of the cophenetic matrix.…”

Genetic Control of White Leaf Spot Resistance and Association Mapping in Corn

“…Considering the above, in plant breeding programs, the characterization of their resistance sources must first be performed in order to make the selection process efficient, since the character genetic control can vary between different resistance sources (Lopes et al 2007;Kaefer et al, 2019).…”

“…In Brazil, the main causes of discontinuity of commercial corn hybrids are new disease epidemics or new strains of pre-existing pathogens previously considered of no economic importance. This is mainly due to the use of susceptible hybrids, monoculture, breeding with no selection for disease resistance, and changes in production systems such as no tillage planting and late growing season (Silva et al, 2015;Kaefer et al, 2019). This is the case of white leaf spot (WLS -Phaeosphaeria maydis (P.…”