Host/parasite relations up to the time of tuber initiation in potato plants infected with Verticillium spp

SUMMARY The growth pattern of potato plants, infected with V. albo‐atrum and V. dahliae, was studied, using growth‐analysis techniques, during the initial stages of development up to tuber initiation. During the first 5–6 weeks of growth the morphology of the infected plants was not affected, but the distribution of dry weight materials between various plant organs and the growth rates of the whole plants were affected much sooner. In contrast to healthy plants, those infected exhibited lower specific leaf areas, higher leaf weight ratios and higher leaf area ratios, and, under dry conditions, lower relative growth rates and lower unit leaf rates. Thus during the incubation phase of the disease, although effects of infection are not immediately apparent, Verticillium pathogens have a considerable influence upon the development of the host.