Effects of irrigation and Verticillium dahliae on cauliflower root and shoot growth dynamics

Cauliflower root and plant growth and Verticillium wilt development were ev aluated under different moisture regimes in the presence or absence of V. d ahliae. Treatments included two main plots (V. dahliae-infested and fumigat ed), two subplots (furrow and subsurface drip irrigation), and three sub-su bplots (deficit, moderate, and excessive regimes) that were arranged in a s plit-split-plot design in the field. Soil cores with roots were periodicall y sampled at 5 and 25 cm distance from plants. Total roots in each soil cor e were extracted with a hydropneumatic root elutriator, and root length fro m each sample was determined with a digital image analysis system. Incidenc e and severity of Verticillium wilt, plant height, number of leaves, and dr y weights of leaves and roots were determined on 10 plants sampled at 7- to 10-day intervals 1 month after cauliflower transplanting and continued unt il harvest. To evaluate the effects of Verticillium wilt-induced stress on cauliflower plants, stomatal resistance was measured in upper healthy and l ower (or diseased) leaves. Root length density at 5 and 25 cm from plant wa s significantly (P < 0.05) higher in subsurface drip than in furrow irrigat ion. Root length density was significantly higher in excessive irrigation r egime than in the other regimes. Concomitantly, there was higher wilt incid ence and severity in excessive and moderate regimes than deficit regime reg ardless of the irrigation method. Plant height was affected by irrigation m ethods and deficit regime. Neither the method of irrigation nor the quantit y of water affected the other variables. Stomatal resistance in lower disea sed leaves was significantly higher in-infested than in fumigated plots but it was not in the upper healthy leaves. In this study, cauliflower yield w as not affected by V. dahliae and irrigation method, but the deficit irriga tion regime resulted in reduced yield even though it suppressed wilt in cau liflower. Thus, higher moisture levels resulted in higher root length densi ty in R dahliae-infested plots that in turn lead to greater incidence of Ve rticillium wilt and severity. The pathogen also affected physiological proc esses such as hydraulic conductance of cauliflower leaves, but not shoot gr owth or yield under these experimental conditions.