2.7.27
EFFECT OF VESICULAR-ARBUSCULAR MYCORRHIZAE ON TOMATO (LYCOPERSICUM ESCULENTUM) IN SOIL NATURALLY INFECTED WITH FUSARIUM OXYSPORUM F. SP. RADICIS LYCOPERSICI

A K GARDEZI1, R GARCIA ESPINOSA1, R FERRERA CERRATO2 and M LARQUE-SMVEDRA3

1Especialidad de Fitopatologia, Instituto de Fitosanidad, Colegio de Postgraduados, 56230 Montecillo, Mexico; 2Area de Microbiologia, Especialidad de Edafologia, Instituto de Recursos Naturales, Colegio de Postgraduados, 56230 Montecillo, Mexico; 3Universidad Autonoma Metropolitana (UAM-AZC), Mexico

Background and objectives
Tomato (Lycopersicum esculentum Mill.) is the most important vegetable crop in Mexico and one of the crops with the greatest relevance world-wide. In 1988, 30% of the vegetable exports from Mexico was tomato, with an estimated value of 200 million dollars [1]. The cutivated area for vegetables has decreased in Mexico in recent years, including the area where tomato is grown. This is due to marketing difficulties and to the increase of phytosanitary problems with (Fusarium oxysporum f. ;sp. radicis Lycopersici (FORL), as reported in the Sinaba Valley where losses have reached up to 100%. The first studies on the interaction of phytopathogenetic fungi and VA were done by Safir [2]. Caron et al. [3], using VA Glomus intraradicis found satisfactory results against F. ;oxysporum f. ;spĚradicis Lycopersici FORL.

Materials and methods
The experiment was conducted under greenhouse conditions. The treatments were distributed in a factorial experimental design (3x2x2), where the factors were: mycorrhiza, (Ml; Glomus sp. Zac-19, M2; Glomus aggregatum and MO, without the mycorrhiza); pasteurized soil, FO; and natural soil, Fl. Two genotypes of tomato, Rio Grande and Ace-55, were used. Each treatment had 10 replications, with a completely randomized design . The variables evaluated were: plant height, stem diameter, number of fruits, fresh weight of fruits, dry weight of aerial parts, root volume, and dry weight of roots.

Results and conclusion
Highly significant differences were observed with the mycorrhiza treatment for the variables plant height, stem diameter, number of fruits, fresh weight of fruits, dry weight of the aerial parts, root volume and dry weight of roots. Mycorrhiza inoculation promoted improvements in all the treatments, but it was particularly stimulating on the plants cultivated in naturally infested soil. The increase of 466% in fresh weight of fruits for the genotype Rio Grande and 358% for the ASE-55 is an indication of the protection of the mycorrhiza against the edaphic pathosystem containing FORL, even though, owing to the greenhouse conditions, the plants did not show the damage commonly observed in the field. In contrast to the control, yreatment 8 (G2-Fl-M1) showed the best results for most of the variables . The genotype Rio Grande had increases of 207.6% in the variable FN, 358.06% in FWF and 143.58% DWR compared with the sterilized soil without mycorrhiza. To conclude , the application of mycorrhiza (VA) Glomus sp. Zac-19 significantly increased all the variables evaluated.

References
1. Anonymous. 1989. Sintesis Horticola 3, 12-13.
2. Safir, 1968. M.Sc.Thesis, University of Illinois, Urbana.
3. Caron 1986 Canadian . Journal of Plant Pathology 8, 12-13.