The use of rhizotrons to study the interactions between cucurbit roots and soil-borne pathogens

Rhizotrons can enable root growth to be quantified without destructive sampling. Root growth can be analysed in real-time to explore the interactions between roots and soil-borne pathogens. Rhizotrons were constructed from plexiglass sheets separated by thin strips of plexiglass to allow a 4 mm wide growing space. By using Hoagland's nutrient solution solidified with 5% agar, growth of cucurbit roots was examined for periods of up to 7 days, the period over which seedlings are most at risk from infection by pathogens such as Pythium aphanidermatum. Cucurbita maxima × C. moschata hybrids have been shown to tolerate infection by P. aphanidermatum and could therefore be potentially useful rootstocks for grafted cucumber plants. At 25°C in the dark and in the absence of P. aphanidermatum, primary roots of the hybrid variety Hercules grew at 0.78 mm hr^-1, not significantly different from the rate of 0.80 mm hr^-1 in the presence of P. aphanidermatum inoculum in the growing medium. The overall rate of secondary root growth was time^2.5 mm hr^-1 in the absence of the pathogen, significantly greater than the rate (time^1.8 mm hr^-1) when P. aphanidermatum was in contact with the root system. The rate of production of secondary roots decreased from 0.46 roots per hour to 0.30 new roots per hour in the absence and presence of the pathogen respectively. The use of rhizotrons could be of significant assistance in future screening of cucurbit germplasm for potential value as rootstocks in disease management programs.