Produtividade e qualidade de tubérculos de batata sob diferentes regimes de irrigação por aspersão convencional

O sistema de irrigação por aspersão convencional é muito utilizado na suplementação de água na cultura da batata. Pressionado, devido à baixa eficiência de aplicação de água, este têm sido substituído pela irrigação por pivô central e localizada, objetivamente mais eficiente. A adoção de sistemas mais eficientes a programas de manejo de irrigação podem aumentar a eficiência do uso de água da batateira. Diante disso, o presente trabalho objetivou a avaliação do efeito de diferentes lâminas e regimes de irrigação no cultivo de batata durante a estação outono/inverno de 2007, na região Sul do estado de Minas Gerais. O experimento foi conduzido sob delineamento estatístico de blocos casualizados, com parcelas subdivididas e quatro repetições. Nas parcelas as duas frequências de irrigação [F4(quatro dias) e F6(seis dias)], e nas subparcelas as quatro lâminas de irrigação em função do percentual da irrigação total necessária (ITN) [L1: 0,8 ITN (80%); L2: 1,00 ITN (100%); L3: 1,10 ITN (110%) e L4: 1,25 ITN (125%)]. As variáveis qualitativas foram avaliadas pelo teste t, com nível de probabilidade (≤10%) e análise de regressão, considerando os valores dos coeficientes de regressão (R²). O ciclo total foi de 119 dias com evapotranspiração média de 181,0 a 186,4 mm. As menores lâminas aplicadas foram 129,5 mm e 133,3 mm em L1, nas frequências de 4 e 6 dias e as maiores 203,4 mm e 209,3 mm em L4 para as frequências de 4 e 6 dias, respectivamente. As maiores produções de batata graúda ocorreram nas lâminas de irrigação de 0,99 e 1,05 ITN para as frequências F4 e F6. A maior produção total foi obtida em F6, com a lâmina de 1,06 ITN. O maior valor de uso eficiente de água foi de 38,05 kg de tubérculo m-3 de água, obtido com a combinação de tratamentos F6/L2 e o menor 32,89 tubérculo m-3 de água na combinação F4/L1.The conventional sprinkler irrigation system is widely used in water supplementation in the potato crop. This is pressed due to the low efficiency of water application, so it has been replaced by central pivot and trickle irrigation, which is more efficient. The adoption of more efficient systems for irrigation management programs can increase the efficiency of water use on potato crop. In view of this, the study aimed to evaluate the effect of different water blades and irrigation regimes on potato cultivation during the fall/winter of 2007, in the southern region of Minas Gerais state, Brazil. The experiment was conducted in a randomized block experimental design with split plots and four replications. In the plots two irrigation frequencies [F4 (four days) and F6 (six days)], and in the subplots the four water irrigation levels were evaluated, based on the percentage of total irrigation necessary (ITN) (L1: 80% ITN, L2: 100% ITN, L3: 110% ITN and L4: 125 ITN). Qualitative variables were analyzed by t test with a probability level (≤10%) and regression analysis, considering the values of the regression coefficients (R²). The total cycle was 119 days with average evapotranspiration from 181.0 to 186.4 mm. The lower water blades 129,5 mm and 133,3 mm were applied in the treatment L1, in the frequency 4 and 6 days and the higher water blades 203.4 mm and 209.3 mm in the treatment L4, in the frequency 4 and 6 days respectively. The highest yield of great tubers production occurred in water blades of 0.99 and 1.05 ITN and in the frequency F4 and F6. The highest production was obtained in F6, with the water blade of 1.06 ITN. The highest value of efficient water use was 38.05 kg of tuber m-3 of water, obtained with the combination of treatments F6/L2 and the lowest value 32.89 kg of tuber m-3 of water in the combination F4/L1.UFV Depto. Eng. AgrícolaUFV Depto de FitopatologiaUNESP FCAV Depto. Eng. RuralUNESP FCAV Depto. Eng. Rura

Temporary partial breakdown of mlo-resistance in spring barley by sudden relief of soil water-stress under field conditions: The effects of genetic background and mlo allele

This study, carried out under field conditions, assessed the extent to which temporary breakdown of mlo-resistance, following relief of water-stress, was determined by genetic background and mlo allele. Commercial barley cultivars expressing the mlo gene for resistance to powdery mildew (Erysiphe graminis (Blumeria graminis) f. sp. hordei) were tested as well as doubled haploid progeny from spring barley genotypes, a proportion of which were sown in the field in two successive years. Plants were protected from natural rain by a mobile rain shelter and either watered by trickle-irrigation or allowed to dry. Percentage mildew infection resulting from natural inoculum was recorded and the doubled haploid genotypes were classified as resistant, intermediate or susceptible on the basis of their control (watered) treatment scores. In each of the three designated classes, particular genotypes developed infection levels, following relief of water-stress, that were higher than those observed on the well-watered controls. This was found not to be related to the mlo allele as there was no significant difference between the increases observed on resistant plants carrying mlo9 and resistant plants carrying mlo11. Differences in the degree of breakdown of resistance were attributed to genetic background rather than to the specific mlo allele