ABSTRACT

The general pattern of symptoms of Verticillim wilt in cotton is a total or partial loss of turgor, due to development of a vascular occlusion. This obstruction is due to the formation of tyloses, which are formed by expansion of xylem parenchyma cells. These tyloses are formed in the xylem wall and grow to invade the vessel lumen of the roots and stem. Another reason for the decreased water flow in the xylem is due to the development of gels and gums, which are spore-trapping mechanisms that delay or prevent fungal spread. The developments of these structures is due to the presence of mycelia fungi within the xylem and colonize the plant by mycelia growth or by conidial production, traveling with the flow of water due to transpiration and germination in the stem xylem. This fungus invades different xylem through the pits from one vessel to another. Cotton plants treated with Brotomax increase their total content of phenolic compounds and gossypol (and its derivatives) in relationship to control plants, and the extract of this plants have high antifungal capacity or resistance against Verticillium dahliae. This increase of antifungal capacity was higher in stem and roots of cotton plants treated. The increases in the antifungal activity of cotton extracts in plants treated with Brotomax reduce the vessel occlusion. Cotton plants treated with Brotomax showed a mean increase of 773.04 Kg.ha-1 (18.65%), although this data depended on the variety. For example, the increase for Carmen was 337.37 Kg.ha-1 (8.83%) and for Crema 1078.11 Kg.ha-1 (28.28%). Tolerance was also observed to depend on variety, with a mean increase of 0.24 (7.18%), the lowest value being for Carmen 0 (0%) and the highest for La Chata 0.50 (23.07%). These results show that varieties susceptible to disease have a higher increase in visual tolerance, although increase yield due to treatment with Brotomax does not depend on the genetic tolerance of the variety. The increase in yield and tolerance to Verticillium was significant at 0.01%, with a value of correlation of 0.56, which suggest that the tolerance visual is a good index of the production for all the varieties assayed. The differences between varieties and the repetitions was also significant but not between the variety and treatment. These results show that Brotomax can increase cotton yield and tolerance against Verticillium in the different varieties assayed.