Submitted to: Crop Protection Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/4/2018
Publication Date: N/A
Interpretive Summary: Garlic is susceptible to infection by a bulb-rotting fungal pathogen, Fusarium proliferatum. The pathogen is soil-borne, and also can be transmitted in the seed cloves used to propagate the crop. An alternative method of propagation is to plant bulbils, for those garlic varieties that produce them. Bulbils are produced aerially in umbels at the top of the scape common in hardneck garlic varities. We wished to know the degree to which seed cloves were infected with F. proliferatum versus the degree to which bulbils were infected, when both the cloves and the umbels were produced by bulbs previously documented as being infected. In one experiment, 64% of the cloves were infected, versus less than 5% of the bulbils. In the repeated experiment the following year, 34% of the cloves were infected, and the pathogen was not detected when sampling the corresponding bulbils. Although bulbils typically take a year longer to mature into bulbs than do cloves, planting bulbils may represent a way to reduce the rate of infection by F. proliferatum.
Technical Abstract: Bulbs of garlic (Allium sativum) 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 Fusarium 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 25-50%. 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.