Meloidogyne is the most damaging plant parasitic nematode genus affecting vegetable crops worldwide. The induction of plant defense mechanisms against Meloidogyne in tomato by some Trichoderma spp. strains has been proven in pot experiments, but there is no information for tomato bearing the Mi-1.2 resistance gene or for other important fruiting vegetable crops. Moreover, Trichoderma is mostly applied for managing fungal plant pathogens, but there is little information on its effect on nematode-antagonistic fungi naturally occurring in soils. Thus, several experiments were conducted to determine (i) the ability of two commercial formulates of Trichoderma asperellum (T34) and Trichoderma harzianum (T22) to induce systemic resistance in tomato and cucumber against an avirulent Meloidogyne incognita population in splitroot experiments; (ii) the effect of combining T34 with tomato carrying the Mi-1.2 resistance gene to an avirulent M. incognita population in sterilized soil; and (iii) the effect of combining T34 with tomato carrying the Mi-1.2 resistance gene to a virulent M. incognita population in two suppressive soils in which Pochonia chlamydosporia is naturally present, and the effect of T34 on the level of P. chlamydosporia egg parasitism. Both Trichoderma formulates induced resistance to M. incognita in tomato but not in cucumber. In tomato, the number of egg masses and eggs per plant were reduced by 71 and 54% by T34, respectively. T22 reduced 48% of the number of eggs per plant but not the number of egg masses. T34 reduced the number of eggs per plant of the virulent M. incognita population in both resistant and susceptible tomato cultivars irrespective of the suppressive soil, and its effect was additive with the Mi-1.2 resistance gene. The percentage of fungal egg parasitism by P. chlamydosporia was not affected by the isolate T34 of T. asperellum. Frontiers in Microbiology | www.frontiersin.org 1 January 2020 | Volume 10 | Article 3042 Pocurull et al. Additive Effect Trichoderma-Mi1.2 Against RKN Conflict of Interest:The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

Cultivation of Cucumis melo is hampered by soil stresses. Grafting is used to overcome these limitations. Different cucurbits belonging to several genera have been used as rootstocks for melons: Cucurbita, Lagenaria, Luffa, etc. However, negative effects on fruit quality appear in some rootstock-scion combinations. The selection of new resistant rootstocks that do not cause this negative impact in quality is necessary to improve melon cultivation. In this work, we evaluated two rootstocks, closer genetically to melon scions than those usually employed: a) an F1 hybrid between a commercial melon (C. melo subspecies melo var inodorus market class Piel de Sapo) and one exotic accession (C. melo subspecies agrestis var. chinensis) with resistance to Monosporacus cannonballus, the causal agent of melon vine decline, and with a certain level of tolerance to Fusarium oxysporum f sp. melonis race 1.2, that causes Fusarium wilt, and b) an accession of Cucumis metuliferus, highly resistant to M. cannonballus, F. oxysporum 1.2 and evaluated and classified as highly resistant to Meloidogyne spp. in this work. Grafting compatibility of these two selected genotypes with commercial melons was good. All grafted plants displayed higher vigour and earlier flowering than ungrafted plants. Fruits from plants grafted onto C. metuliferus showed similar quality than those from ungrafted/selfgrafted plants. However, fruits from plants grafted onto the F1 (inodorus x chinensis) had in this experiment lower brix degree than the ungrafted controls. The resistance to soil borne pathogens found in C. metuliferus and the good performance regarding plant development and fruit quality of the scions indicate that this species is a promising rootstock for melons.

The effect of molasses alone or combined with Trichoderma asperellum T34 Biocontrol® was assessed on Meloidogyne reproduction, disease severity, and density and activity of soil microorganisms in pot and field experiments. Firstly, molasses application at 1 mL m−2 was assessed in four different textured soils. Secondly, molasses application at 5, 10, 20, and 40 mL m−2, alone or combined with T34, was assessed in pot and field experiments at 10 mL m−2 in two different textured soils. The application of 1 mL m−2 of molasses was effective in reducing nematode reproduction in the loam textured soil but not in sandy clay loam, sandy loam, or clay loam textured soils. Increasing molasses dosage reduced the tomato dry shoot and fresh root weights, producing phytotoxicity at 40 mL m−2. The disease severity and nematode reproduction were reduced between 23% and 65% and 49% and 99%, respectively. In the field experiment, molasses applied at 10 mL m−2 reduced the disease severity and the nematode reproduction in the loam textured soil. The soil microbial density and activity did not increase in sites where the nematode reproduction and the disease severity were reduced by molasses application, irrespective of T34.