César Augusto Brasil Pereira Pinto

Genetic gains for heat tolerance in potato in three cycles of recurrent selection

Practically all potato cultivars grown in Brazil are native to Europe and not fully adapted to the tropical conditions. The purpose of this study was to estimate the genetic gains of three cycles of recurrent selection for heat tolerance in potato. The base population in this study consisted of five Brazilian and five heat-tolerant clones. In the winter of 2006 and rainy growing season of 2007 103 clones were evaluated (eight clones of the base population, 29 of the first cycle, 32 and 30 of the second and third recurrent selection cycle, respectively, and four control cultivars). The genetic gains for tuber traits in both growing seasons were 37.8 % (yield), 13.0 % (weight), 32.4 % (percent of large tubers), 0.8 % (tuber specific gravity) and 16.6 % (general tuber appearance). The percentage of physiological disorders (second-growth tubers and cracking) was also reduced by selection.

Caracterização morfofisiológica de clones precoces e tardiosde batata visando à adaptação a condições tropicais

Os objetivos do trabalho foram avaliar os processos de crescimento, de tuberizacao e de particao de materia seca em tuberculos de clones de batata precoces e tardios ao longo do ciclo vegetativo. Avaliou-se, ainda, a viabilidade do uso desses caracteres morfofisiologicos para a selecao de clones mais adaptados as condicoes tropicais. O trabalho foi desenvolvido em Lavras (MG), na safra das aguas (agosto a dezembro de 2005). Os clones tardios foram mais produtivos que os precoces, devido ao crescimento mais vigoroso, a maior longevidade da area foliar fotossinteticamente ativa, a maior taxa de tuberizacao e ao periodo mais longo para enchimento de tuberculos. Os teores de clorofila a, b e total, a area foliar, a duracao da area foliar, a taxa de crescimento relativo e a taxa assimilatoria liquida para os tuberculos foram relevantes na diferenciacao dos clones tardios e precoces. Sugere-se como estrategia possivel para aumentar a produtividade da cultura da batata em regioes tropicais, a selecao de clones com ciclo vegetativo mais longo.

Sample size for family evaluation in potato breeding programs

Clonal families from a broad genetic base population in the Potato Breeding Program at the Universidade Federal de Lavras (UFLA), Brazil, were used in this trials. Twenty-five families were assessed in a 5 x 5 triple lattice design. Each plot consisted of 30 clones distributed in three rows of ten plants. Tuber yield per plant, percentage of large tubers, mean weight of large tubers, mean medium-sized tuber weight and tuber specific gravity were measured. Three hundred experiments were simulated varying the family sizes from three to 90 clones. The coefficients of experimental variation (CVe), the coefficients of genetic variation (CVg), heritabilities for family mean and the CVg/CVe ratio were estimated. Genetic parameters were stabilized with family sizes as small as six clones, depending on the trait. This indicates that the families can be adequately represented by a small sample of clones. Using the maximum curvature method it is possible to conclude that approximately 30 clones would be sufficient to represent each family, even for traits with the highest CVe. The genetic variance within family was greater than the genetic variance among families for all traits, indicating a favorable potential for within family selection. The correlation coefficients of the family means with the 5%, 10%, 15% and 20% best clones from each family, considering the five traits assessed, were always high, meaning that within the best families generally are the best clones.

Early selection of full-sib potato families

A selecao clonal e o metodo de melhoramento preferencialmente usado no melhoramento da batata (Solanum tuberosum L.). Contudo, esse metodo de selecao somente e eficiente em geracoes avancadas e nao apresenta bons resultados quando aplicado da geracao seedling ate a segunda geracao clonal. Objetivou-se, neste trabalho, verificar a viabilidade da selecao de familias em geracoes precoces e comparar o metodo de selecao entre e dentro de familias com a selecao combinada, sob diferentes intensidades de selecao. Seis experimentos foram conduzidos desde a primeira (PGC) ate a terceira geracao clonal. Na PGC, o delineamento foi DBC com quatro repeticoes e parcelas de 25 plantas. Nas demais geracoes, empregaram-se DBC com tres repeticoes e parcelas de 10 plantas. As variâncias geneticas entre familias foram menores que dentro de familias para todas as caracteristicas, mas as herdabilidades entre familias foram quase sempre maiores. Os ganhos esperados com a selecao entre e dentro de familias foram superiores aos ganhos com a selecao combinada, sob qualquer intensidade. A selecao entre familias deve ter intensidade mais fraca que a selecao entre clones dentro de familias, sendo ela mais eficiente, quando baseada na media dos ambientes.

Seleção assistida por marcadores para teor de matéria seca e açúcares redutores em tubérculos de batata

Early generation selection for clones with high content of tuber dry matter and low levels of reducing sugars is required for potato (Solanum tuberosum L.) processing. Selection of superior clones at early generations became possible with the deployment of genetic markers, and can precisely identify the superior individuals. Therefore, it is necessary to identify genetic markers closely linked to genes of interest to do assisted selection. The aim of this research was to evaluate the efficiency of marker assisted selection with genetic markers previously identified by ANDREU (2004), which are assumed to be associated with dry matter and reducing sugars content in potato tubers. Clones from 20 families were evaluated during the seedling generation (S), first clonal generation (C1) and second clonal generation (C2). The estimated coefficients of correlation for all traits among generations were significant, even though of low magnitude, confirming that selection at early generation based only on phenotypic traits is inviable. A total of sixteen bands were amplified using these markers. However, by multiple stepwise regression, only seven of these bands showed association with the evaluated traits. Moreover, no markers associated with dry matter and reducing sugars content in the C1 were significantly associated with these traits in the C2, suggesting the existence of QTLs x environment interactions. The marker assisted selection resulted less efficient than the phenotypic selection in all cases studied, and thus is not recommended for early generation selection of clones for the processing industry. These results suggest that the markers used are not closely linked to the genes controlling the traits most important for processing. Therefore, it is important to identify new markers closely linked with such traits of interest that could improve the efficiency of marker assisted selection.

Seleção de famílias clonais de batata em diferentes ambientes

A selecao precoce em batata tem sido avaliada ha varias decadas, tendo em vista a importância em discriminar e selecionar clones promissores ja nas primeiras geracoes. Na tentativa de contornar a baixa eficiencia da selecao precoce de clones individuais para caracteres de baixa herdabilidade, esforcos estao sendo despendidos na avaliacao do progresso genetico com a utilizacao de familias nas primeiras geracoes. Conduziu-se este trabalho, com os objetivos de mensurar a interacao entre familias e ambientes e avaliar o progresso genetico com a selecao precoce. Foram avaliadas 22 familias e duas testemunhas em tres locais, em Minas Gerais, no delineamento experimental de blocos casualizados, com tres repeticoes. Foram realizadas analises de variância conjunta, de correlacao e estimados os progressos geneticos. Houve interacao familias x locais altamente significativas somente para o carater peso especifico de tuberculos. O ganho genetico esperado com a selecao na media dos ambientes e mais efetivo para a producao de tuberculos. Os ganhos esperados com a selecao na media dos ambientes sao inferiores aos ganhos com a selecao realizada no proprio ambiente, porem, permite identificar familias com ampla adaptacao.

Selection intensities of families and clones in potato breeding

A selecao de familias nao tem sido um metodo recomendado para a selecao de plantas de propagacao vegetativa. Para verificar sua utilidade no melhoramento da batata, realizou-se uma serie de experimentos em condicoes de temperaturas elevadas (safra das aguas). Trinta familias clonais provenientes de genitores tolerantes ao calor foram avaliadas para producao e peso especifico de tuberculos. Depois de obtidas a geracao seedling (GS) e a primeira geracao clonal (PGC) foram avaliados clones individuais, por mais duas geracoes. Foram realizadas simulacoes de diferentes intensidades de selecao de familias na GS e PGC e intensidades de selecao de clones nas geracoes seguintes. Os resultados indicam que intensidades de 50 e 60% produzem os maiores ganhos. As estimativas da h2 em nivel de familias foram maiores que em nivel de clones, o que confirma a eficiencia da selecao de familias em geracoes precoces. A selecao de familias para peso especifico pode ser realizada em geracoes precoces (GS e PGC), independentemente das condicoes de temperatura que sera realizada a selecao clonal. A selecao sequencial de familias, com intensidades de 60% (SG) e 60% (PGC), promoveria maior eficiencia da selecao de clones na segunda e terceira geracao clonal. No caso de aplicar intensidades mais fortes para aumentar a eficiencia da selecao sequencial (GS e PGC), intensidades fracas devem ser aplicadas na GS e mais fortes na PGC . A selecao de familias para a produtividade de tuberculos poderia ser aplicada na PGC, desde que a selecao de clones individuais nao ocorra em condicoes contrastantes de temperatura.

Repeatability of family means in early generations of potato under heat stress

The selection of potato clones for yield is usually effective from the second clonal generation. It would however be ideal to select from the seedling generation (SG) or the first clonal generation (FCG). The aim of this study was to evaluate the repeatability of selection at the family level performed in the early generations with the subsequent generations, for tuber yield and specific gravity in the warm season. Thirty families were evaluated in the SG, FCG and the second, third and fourth clonal generation, without any selection. In this way, adjusted means of the 30 families were obtained for each generation. Selections were simulated independently in the different family generations, and then the repeatability of these families among generations verified, using the same selection intensity. The results showed that the family selection in the SG and FCG for specific gravity and in the FCG for tuber yield is efficient, at mild as well as warm temperatures.

Seleção de famílias para aparência dos tubérculos e tolerância a temperaturas elevadas em batata

Family selection is a method which allows a greater efficiency in breeding programs, since the lower performance families are discarded and focuses are thrown on those most promising families. The aim of this study was to evaluate the efficiency of family selection for traits of tuber appearance and tuber yield under warm and mild temperatures. In this study families were generated by biparental crosses between heat tolerant clones and commercial cultivars with and good tuber appearance. Traits of tuber appearance, tuber yield and tuber specific gravity were evaluated in the seedling, first and second clonal generations. Regarding the traits of tuber appearance some families presented higher frequency of superior clones in the seedling generation. In the first and second generations heat tolerant families were identified which showed positive responsiveness to mild temperatures for tuber yield and tuber specific gravity. It was concluded that family selection for tuber yield and tuber specific gravity was efficient, but family selection for all traits related to tuber appearance was less effective.

Resposta à regeneração e crescimento de brotos in vitro de Kielmeyera coriacea quando influenciado por diferentes concentrações dos sais e de sacarose

Trials were carried out to test sucrose and salt concentrations added to growth medium on regeneration and growth response of Kielmeyera coriacea shoots. The reduction and increase of sucrose of 30 and 45g/l, rerspectively, caused a decrease in total number of shoots. A higher shoots percentage of with more than 1.0cm, occurred on media with 30g/L of sucrose. The use of total force (1/1) and half strength (1/2) of MS salt proportioned a higher shoot ratio and growth.