Pulp composition and the invasion and decay of fruits by microbes

Abstract

Among temperate-zone plant species, fruits with fat-rich pulp have been predicted to disappear more rapidly than low-fat fruits, in part because of more rapid decay by microbes. The influence of fat content of pulp on the susceptibility of fruits to microbial invasion and the rate of pulp deterioration after invasion were examined using Cornus amomum fruits (approximately 5.8% crude fat) and C. racemosa fruits (approximately 23.1% crude fat). Fruits were surface sterilized, punctured with a sterile needle or left undamaged, and inoculated with sterile water, a suspension of bacteria, or a suspension of fungal spores. The two species did not differ significantly in the number of days to first deterioration (= susceptibility), but whole C amomum fruits deteriorated faster than did whole C. racemosa fruits after invasion was first visible. This difference between species persisted when the difference in mean dry pulp mass was taken into account using an exponential model of pulp decay. The two Cornus species did not differ in rate of pulp deterioration (milligrams dry tissue per day) when a linear model of microbial decay of pulp was used. In these two species, higher fat content of pulp does not yield greater susceptibility to invasion or higher rate of deterioration by microbes.