Effects of biofumigant crop termination methods on suppression of plant-parasitic nematodes

Abstract

Biofumigation is a soil sterilization technique using isothiocyanates (ITCs) generated from naturally occurring glucosinolates (GLs, thioglucosides) in members of Brassicaceae. Efficacy of biofumigation on plant-parasitic nematodes could be affected by the way biofumigant crops are terminated. The objective of this research was to determine biofumigant crop termination method suppressive to Meloidogyne spp. and Rotylenchulus reniformis on zucchini (Cucurbita pepo). Three field trials were conducted where ‘Sodbuster’ oil radish (OR; Raphanus sativus) and ‘Caliente 199’ brown mustard (MS; Brassica juncea) were grown as biofumigant crops and subjected to various termination methods. In the first trial (Trial I), OR and MS were each terminated by: 1) clipping off shoots at soil line and covering residues with woven weed mat in no-till (NT); 2) macerating shoots followed by tilling (MT); and 3) MT plus covering with black plastic (MTBP). In the second and third trials (Trials II and III), MS was terminated by: 1) NT; 2) MT; or 3) MTBP, in the same way, described in Trial I; 4) macerating shoots in no-till (MNT); 5) MNT plus covering residues with black plastic (NTBP); and tilling without prior tissue maceration (T). A bare ground (BG) control was included in each trial. Brown mustard MTBP suppressed soil populations of Meloidogyne spp. (Trial I-III) or R. reniformis (Trial I), reduced severity of root galls (Trial I-II) and increased zucchini canopy (Trials I and III) (P ≤ 0.05). None of the OR treatments suppressed Meloidogyne spp. and R. reniformis, but MT and MTBP reduced severity of root galls and increased zucchini canopy (Trial I). When soil glucose and sulfate were analyzed as indicators of biofumigation efficacy, sulfate depicted biofumigation efficacy in the order of MTBP > MT > T, higher than in no-till treatments (NT, MNT, and NTBP) and BG. A similar trend in the glucose was observed only when toluene (methylbenzene) was added immediately to soil samples to arrest microbial degradation of glucose. In summary, Meloidogyne spp. were sensitive to biofumigation than R. reniformis. Biofumigation effect was stronger with MS than OR, and MTBP was the most suppressive treatment on the targeted nematodes. Soil sulfate was more stable in the soil than glucose, thus a good indicator of biofumigation.