The occurrence of Aspergillus flavus in vegetative tissue of cotton plants and its relation to seed infection

Abstract

Twenty-seven mature cotton bolls with Aspergillus flavus Link colonies naturally occurring on the surface of the boll or lint were collected in the field in Arizona along with their subtending stems and peduncles. Bolls inoculated through the carpel wall 30 days after anthesis were allowed to mature in the field and were collected in the same manner. The seed and stem and peduncle sections of each boll were surface-sterilized, plated on agar media and observed for A. flavus. Seventy-eight percent of the naturally contaminated bolls with A. flavus in the seed also had the fungus in the stem and peduncle, whereas only 31% of the naturally contaminated bolls with no A. flavus in the seed had the fungus in the stem or peduncle. This difference was significant (P = 0.0125), indicating a positive relationship between seed infection and stem and peduncle infection. All of the bolls inoculated through the carpel wall had A. flavus in the seed, but only 11% of the stem and peduncle sections were infected, indicating that the fungus does not readily grow downward from the boll into the supporting stem or peduncle. This unidirectional pattern of movement (upward) was further substantiated in greenhouse experiments where cotton seedlings were inoculated at the cotyledonary leaf scar with A. flavus and plants were sequentially harvested, surface sterilized and plated. Aspergillus flavus was isolated from the cotyledonary leaf scar, flower buds, developing bolls, and stem sections in the upper portion of the plant. It was never isolated from roots or stem sections below the cotyledonary node, again indicating that the fungus does not readily move downward through the plant.

Aspergillus flavus: the major producer of aflatoxin

“…In cotton, the mould appears to enter the plant at or before flowering. The fungus does not appear to enter through the stigma, but rather enters from nectaries or other natural openings below the ovary and then moves upward into the developing boll (Klich and Chmielewski, 1 985; Klich et al ., 1984, 1986). Ultrastructural evidence indicates that the fungus may be entering the seeds via the vascular tissue (Huizar et al ., 1990).…”

The Degree of Susceptibility of Nectary-Inoculated Cotton Flowers and Bolls to Subsequent Seed Infection by Aspergillus flavus Is Determined at or before Anthesis

“…This is a period of very rapid plant growth. Our previous field work has indicated that one entry route for A. flavus into cotton bolls may be through vascular tissue (8,11,12). Physical differences between vascular tissue supplying early-season bolls and that supplying later-season bolls may provide an explanation for the results shown in Fig.…”

The effect of aflatoxins on the electron transport chain of chloroplasts fromZea maysL. andPisum sativumL.

“…It has been demonstrated that there is a systemic transmission of Aspergillus flavus in leaves, stems and roots at all stages of growth in maize plants, from developing seeds to harvest (Kelly 1987, Mycock et al 1990. A. flavus movement through the vegetative tissues, has also been reported in cotton (Klich et al 1986). Mycock et al (1992) pointed out that the form th&\ A. flavus var.…”