Study On Control Technology Of Meloidogyne Incognita In Tomato

Root-knot nematode are among common plant parasitic nematodes that cause disease on host from more than 3000 kinds of plants, including vegetables, grain, fruit tree crops, and ornamental plants as well. From the point of regional distribution of disease, situation of tropical and subtropical plant species is more serious than other areas. Due to root-knot nematode infestation the production of crop is decreased by 10%20%, sometimes even causes 75%, crop failures. With the development of horticultural facilities in China, the area of protected horticulture is now much larger than before; however, the multiple cropping index and continuous cropping lead to occurrence of root-knot nematode. Although there are many ways to prevent and control root-knot nematode, such as chemical control, physical control, biological control, resistance breeding, etc., these methods have their own advantages and disadvantages. Therefore, seeking a safe, effective and sustainable way to decrease the root-knot nematodes is very important. In this study, we used several tomato (Solanum lycopersicum L) varieties and their mutants as plant materials, and also applied various techniques including grafting, virus-induced gene silencing (VIGS), LED light and graminaceae companion cropping experiments, to elucidate the mechanisms controlling southern root-knot nematode resistance. Main results are as follows:1. Studies have shown that jasmonic acid (JA) play an important role in tomato tolerance to southern root-knot nematode, where the JA mainly originated from leaves. JA level was induced upon root-knot nematode infestation. Compared with wild type, the JA deficient mutant (spr2) and JA signaling mutants (PI Ⅰ, PI Ⅱ) of tomato both showed increased root-knot nematode sensitivity, the plants were more vulnerable to nematode infection. The number of root knot(galls) in spr2/WT was more than that in WT/spr2 grafted tomato plants following inoculation with nematodes, indicating that the content of JA in the leaves (scion) is important than the underground parts in the grafted plants for induction of resistance against root-knot nematode.2. Studies have shown that hydrogen peroxide (H2O2) significantly improved root-knot nematode tolerance in tomato. We measured the H2O2 accumulation in the root of tomato plants after inoculation with root-knot nematode, and found that the H2O2 content in root was increased gradually, and reached a peak in the third day, then began to decline. In addition, number of galls caused by root-knot nematode in RBOH-RNAi plants was more than that in the wild type plants, while H2O2 accumulation in both stems and leaf RBOH-RNAi plants were lower than that in wild type. This implies that H2O2 is essential for the induction of resistance against root-knot nematode in tomato. In other words, tomato plants deficient in H2O2 would be more susceptible to root-knot nematode.3. Examined whether light quality had any effect on the resistance to root-knot nematode. Using 6 different light quality treatments such as the white, red, blue, the combination of white light and far red light, red light and far red light, blue light and far red light, we found that red light could induce the JA accumulation and markedly improved the tolerance of tomato plants to root-knot nematodes compared with the white or blue light. Meanwhile, far red light increased the sensitivity to root-knot nematode and suppressed the effect of red light. By screening the resistance of different light receptor mutants, we noticed that phyB1B2 mutant was most susceptible to southern root-knot nematode compared with all other tomato genotypes. In addition, we grafted different phytochromes mutants and wild type tomato as scions on wild type root-stock and inoculated with root-knot nematode. Results showed that the levels of JA in leaves and roots of phyB1B2 mutant(scion)-grafted tomato plants were significantly lower than that in wild type as scion. Taken together, these results suggest that red light induces resistance against root knot nematodes by promoting JA level, while plants perceive red light signals through the action of PHYB photoreceptors.4. Studies have shown that companion cropping with wheat, barley and rice effectively alleviated the sensitivity of tomato to root- knot nematode. Companion cropping with graminaceous species decreased the index of galls and eggs, the numbers of eggs and two age nematode in 100 g rhizosphere soil compared to control in tomato plants. Among all the treatments, the effect of barley was the most obvious, as indicated by the index of root knot and eggs dropped by 73.3% and 82.1%, respectively, and the number of eggs in 100g rhizosphere soil decreased by 66.9%, meanwhile, the loss rate of nematode mouth spear(stylet) was 48.4%.