Antagonistic potential and histopathology of Meloidogyne javanica on Macrotyloma axillare cv. Java

Root-knot nematodes are obligate parasites, so changes at their feeding sites can limit their development. Alterations to feeding sites is one of the main actions taken by antagonistic plants. The aim of this study was to assess the response and histopathology of interactions between Meloidogyne javanica and the roots of Macrotyloma axillare cv. Java. The penetration and development of the nematode was assessed from 8 to 30 days after inoculation (DAI) with 3000 eggs + second-stage juveniles (J2) of M. javanica. The reproduction factor (RF) was assessed at 60 DAI, with two inoculation levels, 700 and 1000 eggs + J2, and the changes in the development and histopathology of M. javanica was assessed at 10, 15 and 30 DAI. Suscetible soybean was used as a control. The development of nematodes at the third (J3) and fourth juvenile (J4) stages was delay, despite the presence of J2 inside the roots, and no adult females were found in the M. axillare cv. Java roots. RF was 0.31 and 0.39 for M. axillare cv. Java and 3.40 and 4.52 for soybean at inoculation levels of 700 and 1000 eggs + J2, respectively. The feed cells in M. axillare cv. Java could not effectively nourish the nematode, which led to deformed females 30 DAI. The feed cells and nematode development, however, were normal in soybean. M. axillare cv. Java was resistant to M. javanica and had an antagonistic potential, because it did not prevent the nematode from penetrating the roots but had a negative effect on M. javanica due to the inefficiency of the feeding site.

Crotalaria and millet as alternative controls of root-knot nematodes infecting okra

The relationship of crops grown in rotation or in succession has increased every day and the use of antagonistic plants and/or non-host plants is one of the most efficient practices of integrated management of nematodes. This study aimed to evaluate the efficiency of crotalaria (Crotalaria spectabilis Roth) and millet [Pennisetum glaucum (L.) Leeke] ‘ADR 300’ in reducing the population of Meloidogyne incognita and M. javanica and in increasing the productivity of okra [Abelmoschus esculentus (L.) Moench] when cultivated in succession. The experiment was conducted in an area cultivating okra (host culture) in rotation, with a history of severe infestation by phytonematoids. The experimental design involved randomized blocks with six treatments and four replicates, with the following treatments: T1, 15 kg.ha-1 of millet seeds; T2, 30 kg.ha-1 of crotalaria; T3, 10 kg.ha-1 of millet + 20 kg.ha-1 of crotalaria; T4, 20 kg.ha-1 of millet + 6 kg.ha-1 of crotalaria; T5, 6 kg.ha-1 of millet + 36 kg.ha-1 of crotalaria; and T6, control. The nematode populations in the soil and roots were evaluated about 60 d after planting okra, and the yield was evaluated at the end of the crop cycle. Simple treatment with millet or crotalaria reduced the nematode population by 61% and 72%, respectively. The millet-crotalaria intercropping treatments reduced the nematode population by up to 85% compared with the control. In terms of productivity, there was an increase of 787 kg.ha-1 in the millet treatment and 2,109 kg.ha-1 in the intercropping treatments. Both the single cultivation of crotalaria or millet and the consortia of crotalaria and millet were effective in controlling the root-knot nematodes, and increased the productivity of okra.

REPRODUCTION OF Pratylenchus zeae AND P. brachyurus IN COVER CROPS

ABSTRACT This study aimed to evaluate the reproduction of Pratylenchus zeae and P. brachyurus in leguminous plants used as cover crops. Seedlings of sunn hemp (Crotalaria juncea and C. spectabilis), pigeon pea cultivar IPR 43 (Cajanus cajan), dwarf velvet bean (Mucuna deeringiana), black velvet bean (Stizolobium aterrimum), and jack bean (Canavalia ensiformis) were inoculated with each nematode separately. Maize cultivar IPR 114 and soybean cultivar Pintado were used as controls to measure the viability of the inoculation of P. zeae and P. brachyurus. After 90 days of inoculation, the plants were collected and nematode g-1 root, final population, and reproduction factors (RF) were evaluated. The experiment was carried out at two different times of the year. The nematode’s RF on cover crops from treatments with the two Crotalaria species, dwarf pigeon pea, and black velvet bean were lower than one (bad host plants) in both experiments for P. zeae. For P. brachyurus, the lowest RFs were obtained for C. juncea, C. spectabilis, and pigeon pea, while the other plants presented RF values close to or higher than one in at least one of the experiments. Therefore, C. spectabilis, C. juncea, and C. cajan cultivar IPR 43 are antagonistic plants that represent useful options for rotation or succession systems that aim to control P. zeae and P. brachyurus.

Antagonistic Effects of Java against Plant Parasitic Nematodes

One of the main phytonematode control alternatives is the use of antagonistic plants in crop rotation or succession systems. Although java legume shows antagonist potential to control Meloidogyne javanica, its reaction to other nematodes was not investigated so far. Thus, the aim of the current study is to assess the penetration and reproduction factor (RF) of M. incognita, Rotylenchulus reniformis and Pratylenchus brachyurus in java, using soybean as control. Plants individually inoculated with 1000 specimens from each nematode were assessed 5, 10, 15, 20, 25 and 30 days after inoculation (DAI) for nematode penetration and development. The RF was assessed under two inoculum levels of each nematode (1000 and 700 specimens) 60 days after inoculation, for M. incognita and R. reniformis; and 80 days after inoculation, for P. brachyurus. Meloidogyne incognita and R. reniformis showed lower penetration and reproduction in java (RF < 1), whereas P. brachyurus showed higher penetration and RF > 1. Thus, the java legume can be considered resistant to M. incognita and R. reniformis, as well as susceptible to P. brachyurus.