Density-dependent Growth Patterns of Meloidogyne javanica on Hemp Cultivars: Establishing Nematode-sampling Timeframes in Host-status Trials

Abstract

The timeframe host plants should be exposed to Meloidogyne species prior to nematode sampling for host-status and/or host-sensitivity is indispensable in interpretation of results and the subsequent management decisions. The aim of this study was to use density-dependent growth patterns of population density of M. javanica infecting hemp (Cannabis sativa) cultivars to determine the timeframe from inoculation to nematode-sampling in host-status trials. Seedlings of four hemp cultivars ‘Kompolti’, ‘Futura-75’, ‘Ferimon’ and ‘Felina-34’ were each inoculated with 1000 second-stage juveniles of M. javanica under greenhouse conditions, with four cultivars (main-plots) and five biweekly nematode-sampling times (sub-plots) arranged in a split-plot design, with five replications (n = 100). Interaction and cultivar type had no significant (P = .05) effects on population density of M. javanica, while increasing sampling time had highly significant (P<.001) effects on variables, contributing 63%, 54% and 59% to total treatment variation on population density of female, male and juvenile, respectively. Nematode population density (y-axis) and increasing sampling time (x-axis) had strong density-dependent growth relations as depicted by the coefficients of determination of the quadratic equations on females (R2 = 0.50-0.82), males (R2 = 0.47-0.89) and juveniles (R2 = 0.64-0.93). Female population densities of M. javanica were optimized at 56 days on cultivars ‘Kompolti’, ‘Futura-75’ and ‘Ferimon’, while on cv. ‘Felina-34’ optimization occurred at 151 days. Generally, there was a time-lag in optimization of males and juveniles, suggesting that they were not suitable determinants of the nematode sampling time. In conclusion, the derived empirically-based nematode sampling timeframes would facilitate comparisons of results and also resolve an assortment of challenges in host-status and/or host-sensitivity trials. The procedure could also be used to develop timeframes of Meloidogyne species in other crops or in other nematode-plant relations.