L.P.G. Molendijk

Tagetes patula as an effective catch crop for long-term control of Pratylenchus penetrans

Tagetes patula is well known to be able to diminish Pratylenchus penetrans (Cobb) populations. In a field experiment, the increase of the P. penetrans soil population density after growing T. patula was significantly less than after chemical soil fumigation with metam sodium. The effect of T. patula on P. penetrans population densities lasted longer than the effect of chemical soil fumigation. Strawberries were grown for 3 consecutive years after T. patula without damage by the root lesion nematode. Assuming a linear rate of increase of the P. penetrans population density, we predict that strawberries could be grown for about 7 successive years without economic damage due to the root lesion nematode. Strawberry yield was greater from the crop grown 3 years after T. patula than that after soil fumigation 4 years previously. About 2 t strawberry yield increase is necessary to allow the growth of Tagetes every 5th year, without economic loss. The possibility of growing both strawberries and Tagetes in the same year should be investigated.

Tuber and root resistance of potato genotypes against Meloidogyne chitwoodi in the presence of Avena strigosa, related to tuber quality

Relative tuber infestation and quality of two Meloidogyne chitwoodi resistant potato genotypes, AR04-4096 and 2011M1, were compared in glasshouse experiments at initial population density (Pi) = 16 second-stage juveniles (g dry soil)−1 in the presence and absence of the bristle oat, Avena strigosa. When A. strigosa was added, Pfroot+soil (Pf= final population) on both AR04-4096 and 2011M1 increased 130×, Pftuber increased 1.9 and 3.7×, respectively, while Pftuber × fresh root weight (FRW)−1 was the same. Nematode hatch from peel of AR04-4096, without A. strigosa, was delayed by 3 weeks but relative hatching rate was increased. Although the RStuber (RS = Relative Susceptibility) of both AR04-4096 and 2011M1 were lower than 1%, in the presence of A. strigosa tuber quality of 2011M1 dropped below the marketable level, while that of AR04-4096 was hardly affected. We conclude that: i) Pftuber is influenced by root mass; ii) root quality influences nematode hatch; iii) tuber quality is not an estimator for tuber resistance, and the reverse; iv) root resistance is equal to tuber resistance.

A routine test for the relative susceptibility of potato genotypes with resistance to Meloidogyne chitwoodi

The population dynamics of Meloidogyne chitwoodi on eight potato genotypes was compared to the susceptible cv. Desiree in four glasshouse experiments. The initial nematode densities consisted of log series 2x , with −4 < x < 8. Seinhorst’s logistic model was fitted to the final population densities to estimate the parameters maximum multiplication rate (a), maximum population density (M) and the ratios RSa, RSM and M/a. Average RSa and RSM of the seven resistant genotypes were smaller than 0.29%. The M/a ratios on six resistant genotypes and cv. Desiree were the same, 1.3, indicating Pi independence of RS. One genotype stood out with M/a = 8.6, whereby RSa < RSM. Both RS and M/a were unaffected by pot size or experimental conditions. Screening protocols at Pi = 24 second-stage juveniles (g dry soil)−1 in 2 or 3 kg pots were evaluated for distinctiveness between the two genotype groups. Based on the results, an optimal protocol for a routine resistance test is proposed.