Evaluation of eleven cucumber hybrid’s reaction to root-knot nematode (Meloidogyne incognita) in greenhouse conditions

Background and Objectives

Cucumber (Cucumis sativus L.) holds significant agricultural importance in Iran, occupying extensive cultivation areas. Greenhouse conditions favor the proliferation of numerous pests and diseases affecting cucumber growth. Root-knot nematodes inflict yearly damage on cucumber farmers and producers, particularly in tropical and subtropical regions. Cucumbers are susceptible to various plant-parasitic nematodes, with Meloidogyne species, notably root-knot nematodes, posing significant threats. Controlling the nematode is challenging due to its wide host range, short life cycle, high reproductive rate, and parasitism. While chemical control remains prevalent for nematode population management, growing public concern over the environmental and human health impacts of nematicides is driving efforts to restrict their usage. Employing resistant varieties either independently or in conjunction with other strategies is increasingly recognized as a highly effective means of nematode control. Resistant plants prevent the need for long-term rotations and are highly suitable for sustainable agriculture. Consequently, the development of new cucumber varieties and hybrids and the assessment of their resistance can be applied in integrated nematode management. Hence, this research aims to evaluate the resistance of cucumber hybrids to root-knot nematodes (M. incognita) under greenhouse conditions.

Materials and Methods

Soil and root sampling was undertaken from cucumber cultivation sites in Guilan province. Egg masses were then introduced to the root systems of tomato seedlings, specifically the Early Urbana variety, at the two to four true leaf stage. Subsequently, these seedlings were nurtured for 45 to 60 days under greenhouse conditions. Identification involved the analysis of perineal patterns alongside morphological and morphometric traits of second-stage juveniles. Staining of female nematodes in root tissue was accomplished using the Hartman and Sasser method. Multiple consecutive inoculation cycles were executed on susceptible tomato plants to cultivate a substantial and uncontaminated nematode population. Seed germination took place in Petri dishes, with transfer to individual pots containing a mix of perlite and coco peat in equal measures after 48 hours. These pots were then randomly distributed within the greenhouse, with subsequent maintenance performed as required. The experiment followed a completely randomized design with three replications. Ten weeks post-inoculation, nematode-related parameters, such as the count of galls and egg masses using the Taylor and Sasser method, alongside the number of second-stage juveniles in the soil using the Barker method, were assessed. Subsequently, statistical analysis was carried out utilizing SAS 9.0 software following data normalization. Mean comparisons were conducted using the Tukey test.

Results

The results showed significant differences in some traits of the hybrids treated with nematodes. Variance analysis revealed no significant differences in specific indicators, including gall count, egg sacs, eggs, second-stage juveniles in the soil, reproduction factor, as well as fresh and dry shoot and root weights across the assessed hybrids. However, significant differences were observed among the growth indices of plants, particularly in fresh and dry shoot weight, fresh root weight, and root volume. The mean weight of the aerial parts in the control was 103.66 g. Hybrid 5×3 exhibited the highest reduction, with a weight of 63.33 g, reflecting a 38.9% decrease compared to the control. Conversely, hybrid 7×6 showed the least disparity, with a weight of 100 g and only a 3.53% reduction. Notably, significant differences were evident in gall index, egg mass index, resistance index, root dry weight, and root length. According to the Taylor and Sasser ranking for determining gall and egg masses indices, hybrid 2×6 exhibited sensitivity, while the remaining hybrids were classified as very sensitive. Regarding the egg masses index, hybrids 5×3, 2×6, and 3×4 displayed relative resistance, whereas the other hybrids were categorized as sensitive. Evaluation based on the reproduction factor and gall index indicated that all hybrids were classified as sensitive.

Discussion

The study concluded that none of the hybrids exhibited significant resistance indices. However, hybrid 2×6 demonstrated statistical significance in gall index, egg masses, and resistance, while hybrid 2×7 displayed superiority over the control variety in terms of larval count, egg count, and dry shoot weight. Consequently, pending further complementary experiments, these hybrids may be regarded as promising replacement candidates.