Infection by Fusarium proliferatum in aerial garlic bulbils is strongly reduced compared to rates in seed cloves when both originate from infected bulbs

Abstract

Infection of bulbs of garlic (Allium sativum) by Fusarium proliferatum is increasingly documented worldwide and management of the pathogen is problematic. Garlic bulbs were harvested at the USDA-ARS Plant Introduction farm near Pullman, WA in fall 2015. From a sample of 18 bulbil-producing accessions whose bulbs were documented as infected by F. proliferatum, a mean of 64% of cloves from infected bulbs contained the pathogen. In umbels produced from infected bulbs, a mean of 11% were detected with the pathogen, with a mean infection rate of bulbils in infected umbels of 42%, resulting in a probability of bulbil infection of less than 5%. In bulbs harvested in fall 2016 from 15 accessions whose bulbs were previously documented as infected, a mean of 34% of cloves in infected bulbs contained the pathogen, but the pathogen was not detected in umbels or bulbils. Overall incidence of F. proliferatum in bulbs surveyed for infection in 2016 (99 accessions) at the same farm was assessed via a cumulative geometric distribution, and indicated occurrence in 87% of accessions, with probability of infection in a given bulb between 25 and 50%. In 2016, all but 0.01% of whole bulbs harvested for this survey of overall incidence were asymptomatic at harvest on the basis of firmness, but 77% of cloves were symptomatic (inclusive of all biological and abiotic causes) when peeled and plated to agar media 9–16 months after harvest. Bulbils take at least a year longer to mature into full size bulbs than do seed cloves, presenting a longer window for infection by several pathogens, but if planted to pathogen-free soil might represent a cost-effective means to strongly reduce infection of propagation material by F. proliferatum.