The influence of potato cyst nematodes (Globodera pallida W.) and drought on rooting dynamics of potato (Solanum tuberosum L.)

Minirhizotron root video observations of two experiments (in 1991 and 1992) in the Wageningen Rhizolab were used to investigate the extent to which potato cyst nematodes (Globodera pallida) without (1991) or with accompanying drought (1992) influenced the rooting dynamics of potatoes. The main effect of potato cyst nematodes in 1991 was a retarded root length. At a depth of 10 cm and without nematodes, the maximum total root length was produced 60 days after planting. At a depth of 45 cm, this point was reached after 80 days. With nematodes (2.5, 10 and 40 living larvae per gram of soil ), however, the date at which maximum root length was produced was retarded with at least 20 days, depending on the infestation level of the soil. At a depth of 45 cm, nematodes at the highest infestation level also eventually resulted in a shorter root length. At a depth of 10 cm, nematodes resulted in a somewhat greater root length. The effects of nematodes on the longevity of potato roots were analysed by following the fate of individual root segments. It was concluded that in the first experiment (1991), the rate at which roots decayed was higher without nematodes than with nematodes. Combining the data for root length production with root length decay, it was found that without nematodes, the standing living root length was only higher in the first part of the season. Also, from the second experiment (in 1992), in which the effect of nematodes was studied in combination with drought, potato roots did not show a reduced longevity with nematodes. The yield of potatoes in the presence of nematodes is discussed.