The effect of pollen on the fungal leaf microflora of Beta vulgaris L. and on infection of leaves by Phoma betae

Abstract

Studies were made on the leaf-inhabiting fungus flora of two plots of flowering sugarbeet. Flowers were removed from plants of one plot as they appeared. Changes in the numbers of micro-organisms on leaves were recorded by leaf washing and leaf homogenization techniques, and were found to follow closely the changes in numbers of pollen grains seen on cleared leaf discs. The main colonizers, grouped into pink yeasts, white yeasts, Cladosporium spp. and Aureobasidium pullulans, were all influenced by the natural presence of pollen and reached high numbers on leaves in the plot bearing flowers. Rainfall was not found to influence numbers of pollen grains or micro-organisms greatly, but high temperature led to isolation of smaller numbers of pink and white yeasts. Recovery of populations was swift after hot weather, and may be linked with the high contamination of fieldcollected sugarbeet pollen by components of the microflora. The spectrum of fungi growing from washed leaf discs differed qualitatively from assessments made by washing and homogenization.Rye pollen stimulates Phoma betae to aggressive infection of sugarbeet leaves on which, due to the prevention of a natural pollen deposit, the development of the leaf microflora is meagre. Sugarbeet plants in both plots were inoculated with conidia of P. betae with or without added rye pollen. The presence of a dense microflora, associated with a high natural pollen deposit, reduced the incidence of aggressive infection normally stimulated by the addition of rye pollen to inoculum.

The buffering capacity of the natural mycoflora of rye leaves to infection by Cochliobolus sativus, and its susceptibility to benomyl

“…An explanation may be the high temperatures, reached on the days before sampling. Air temperatures of almost 30~ have been found to reduce the colonization by the yeasts (Fokkema, 1971;Warren, 1972a). Therefore the colonization before the warm period might have been higher than the data suggest.…”

“…In nature, dense populations of saprophytes can develop before the onset of senescence on leaves of anemophilous crops. The saprophytic mycoflora on these leaves is stimulated by nutrients released from pollen deposited on the leaf after flowering (Fokkema, 1971 ;Warren, 1972a). In a rye field, pollen also stimulated leaf infection by Cochliobolus sativus, but only for a very short period after flowering.…”

Appetite of an epiphyte: Quantitative monitoring of bacterial sugar consumption in the phyllosphere

“…Exogenous nutrients may be available fortuitously in the form of pollen, honeydew, dust, air pollution, or microbial debris (17,18). Occasionally, plant sap may ooze from wounds inflicted by insect feeding (17) or frost damage (12).…”

Role of Leaf Surface Sugars in Colonization of Plants by Bacterial Epiphytes

“…In order for microbial colonization to occur, a carbon source for energy generation and growth, a nitrogen source, and certain essential inorganic molecules must be present on leaves. Exogenous nutrient sources, such as aphid honeydew and pollen, have been associated with a dramatic increase in the microbial carrying capacities of some leaves (12,40). However, in the common absence of such obvious and abundant nutrient sources, plants are still usually colonized by high numbers of bacteria, which can reach 10 5 to 10 7 CFU per g of leaf under favorable environmental conditions, such as when high relative humidity or free water is present (16,17,33).…”