Genetic parameters and strategies for selecting sugarcane genotypes for borer resistance

• Ano de defesa: 2018
• Autor(a) principal: Tomaz, Adriano Cirino
• Tipo de documento: Tese
• Tipo de acesso: Acesso aberto
• Idioma: eng
• Instituição de defesa: Universidade Federal de Viçosa
• Palavras-chave em Português: Cana-de-açúcar - Resistência a doenças e pragas; Broca-da-cana; Saccharum; Cana-de-açúcar - Seleção; Cana-de-açúcar - Genética; Melhoramento Vegetal
• Link de acesso: http://locus.ufv.br//handle/123456789/26058

The sugarcane borer Diatraea saccharalis (Lepidoptera: Crambidae) is one of the most important pests in sugarcane crops in Brazil and it has been controlled mainly by the use of both biological and chemical control. There is no sugarcane varieties resistant to this pest in Brazil. The lack of knowledge about genetic parameters in Brazilian sugarcane breeding populations and about selection strategies hinders the development of resistant varieties by conventional breeding programs. Therefore, the purpose of this study was to estimate genetic parameters and to compare strategies for selecting sugarcane genotypes for borer resistance. This study was divided in two parts: In the first part, a T1 (originated from true seed) and a T2 (first clonal selection stage) populations were used. In the second part of the study, a population in an experimental stage was used. The T1 experiment aimed to: estimate individual heritability, heritability at family mean level, genotypic variance among families, additive and non-additive genetic effects; and compare individual, family and parents selection. The T2 experiment aimed to: estimate heritability at clone means level and genotypic variance among clones; and assess the efficiency of family selection at T1 stage. T1 experiment was carried out in a randomized block design with 46 full- sib families and four replicates per family. This experiment was established in the year of 2014, at Iturama municipally, Minas Gerais state. In the year of 2015, the infestation index by borer (IIB) was assessed in ten plants per plot, totaling 40 plants per family. In 2016, 32 individuals from the three most resistant and 32 individuals from the three most susceptible families were selected in T1 experiment, to compose de T2 experiment, conducted at Capinópolis municipality, Minas Gerais state. This experiment was carried out in a randomized block design, with five replicates and 64 clones. The IIB was assessed in the year of 2017. In T1 experiment, the heritability at famility means level (h2 = 0.77) was higher than individual heritability (h2 = 0.16). It indicates that family selection is more effective than individual or mass selection. There was difference among family means (18.41 < IIB < 30.41%), indicating the possibility of selecting families for borer resistance. The additive genetic effect is more important than non-additive effects so parents can be selected only through their genetic additive effects. The results of T2 experiment indicated that there is high genetic variance of clones within families (6.63 < IIB < 17.57%). Thus, the selection of families at T1 stage must be followed by clone selection at T2 stage, where the individuals can be assessed in replicated experiments and higher heritability at clone means level can be achieved (h2 = 0.61). The second part of this study aimed to: estimate variance components and heritability; assess the effect of genotype x environment (location, year) interaction in borer resistance; to compare selection strategies; to assess the effect of selection for borer resistance in productivity components (Tons of cane per hectare (TCH), Theoretically recoverable sugar (TRS) and Tons of sugar per hectare (TSH)); and to study the possibility of using selection index for selecting sugarcane genotypes for borer resistance and yield components. A population at an experimental stage with 35 clones, planted in four locations in experiments with 18 or 24 clones and four or five replicates was used. The IIB was assessed in the years of 2015, 2016 and 2017. There was no genotype x year, genotype x location nor genotype x year x location interaction for borer resistance. The heritability in single experiments was moderate or elevated (0.53 < h2 < 0.78) as well as heritabilities for selection in one location and several years (h2 = 0.63), several locations and one year (h2 = 0.74), and several locations and years (h2 = 0.80). Therefore, selection for borer resistance may be performed at only one location and year or by the clones' means in several locations and years. The selection for borer resistance reduced the genetic gains for TCH, TRS and TSH, justifying the use of selection index, which made it possible to obtain satisfactory genetic gains for IIB, TRS and TCH. We can conclude that selection at T1 stage enables selection of families and parents for borer resistance. However, this selection must be followed by clone selection at T2 stage, due to high genetic variability within families. In more advanced selection stages, the clones can be selected either in one location and year or by their means in several years and locations, as there is no genotype x environment interaction. The use o selection index combining IIB, TCH and TRS enables selecting sugarcane for borer resistance in addition to stalk and sugar productivity. Keywords: Diatraea saccharalis, Saccharum spp., heritability.