Ditylenchus destructor is a plant-parasitic nematode that negatively impacts upon garlic production in Japan. It feeds not only on plant cells but also on fungi; hence, fungal infection of garlic plants may also potentially affect nematode propagation. In the present study, we assessed whether or not the nematode could propagate on garlic storage leaves under fungus-free conditions, and thereby cause garlic rot. We detected propagation of nematodes at 4 weeks after the inoculation of axenic nematodes onto surface sterilized garlic storage leaves of Fukuchi white, the major garlic variety cultivated in Japan. In further tests, the nematodes propagated on 16 garlic varieties by 8 weeks post-inoculation, but propagation levels were significantly lower in varieties from southwest Japan, such as Hirado and Iki, than in the varieties Ishikawa roppen and Fukuchi white. Moreover , the garlic storage leaves on which the nematodes propagated most successfully became rotten. These results suggest that D. destructor can propagate on garlic storage leaves and cause garlic rot without the influence of fungal infection.
Photorhabdus luminescens is a gram-negative luminescent enterobacterium that symbiotically resides in the digestive tract of an entomopathogenic nematode (EPN) of the familyHeterorhabditidae. Heterorhabditis bacteriophora upon entering an insect host, regurgitate P. luminescens cells, and the bacteria quickly establish a lethal septicemia. To expand the possibility of its cockroach control, the insecticidal activity of this nematode-bacterium complex against cockroaches was investigated in two ways. First, we examined the insecticidal activity of H. bacteriophora harboring P. luminescens against the middle-stage instar of three Periplaneta (P. fuliginosa, P. americana, and P. japonica) and one Blattella (B. germanica) cockroach species. Mortality of P. fuliginosa and P. americana were significantly increased when treated with 20,000 and 100,000 nematodes/0.3 g bait/ 5 cockroaches. The mortality of P. japonica, however, did not differ from that of the control at all of the tested concentrations; whereas, the mortality of B. germanica was relatively higher than that of Periplaneta cockroaches. Second, we tested the pathogenicity of P. luminescens alone against the three Periplaneta species by injection of bacterial cells. All tested cockroaches were found to be killed within 2–4 days. These results would suggest that Periplaneta are susceptible to P. luminescens; however, in the bait experiment, H. bacteriophora was unable to effectively establish a lethal infection of P. luminescens. Our results indicate that susceptibility to EPN infection and bacterial pathogenicity should be evaluated separately, and that much less H. bacteriophora is required to kill B. germanica than is needed to kill three Periplaneta cockroaches.
To save time and effort in quantifying the newly produced females of Heterodera schachtii (HS), we introduced a simple root box (RB). The RB was composed of two transparent trays, where we examined whether the number of young females on the plant roots in the RB that would be seen from the outside could be used to accurately predict the number of mature females (cysts) in the RB soil. We inoculated 20 to 10,000 individuals of the HS second-stage juveniles into Chinese cabbage seedlings that were planted in the RB. After 20 and 58 days of inoculation at 25°C, we quantified the number of young females that appeared on the roots and the number of mature females (cysts) that appeared in the RB soil, respectively. We detected a high correlation, in which the total number of the HS females that appeared on the roots in the RB was a relatively reliable predictor of the total number of HS cysts in the RB soil. However, we concluded that controlling the moisture and the type of soil in the RB may influence the reliability of the quantification using the RB.
The control effects of applying a solid-type material (carrier: PVA and agar) B. pilosa var. radiata extract onto root-knot formations of M. incognita and M. hapla were evaluated. It was clear, in particular, that the highest controlled effect of the planting hole treatment (bottom side) of the cube-type material, occurred where the rates of agar and plant extract dry matter were 1:3. Furthermore, the control effect of cube-type materials (1:3) on M. hapla was high when the amount of sprinkling water was increased, compared with that used regularly, and no influence on the growth of tomatoes was observed. As a result, the B. pilosa var. radiata extract materials could be used as an environmentally-friendly control agent for M. incognita and M. hapla.