Friday, December 2, 2016

Stem and Bulb Nematode Discovered in New Mexico

Figure 1. Garlic plants exhibiting severe symptoms of stem
and bulb nematode (Photo: J. M. French, NMSU-PDC)
Stem and bulb nematode, Ditylenchus dipaci, discovered on Garlic in the Rio Grande Valley of New Mexico - Ditylenchus dipsaci is a serious temperate-climate nematode pest of over 500 plant species in over 40 plant families, including alfalfa, onions, and garlic.  Among plant-parasitic nematodes, it ranks fifth in economic importance and is a quarantine pest of international concern. In 2015, New Mexico harvested 190,000 acres of alfalfa hay with a value of over $188M and is the eighth largest producer of onions in the U.S. cultivating 5,200 acres in that year with a crop value of $91M. These two crops rank number 1 and number 3, respectively, for highest grossing crops in NM in 2015. New Mexico also has a vibrant small farm garlic industry that supplies local markets with fresh garlic and seed for producers.  New Mexico has never reported an infestation of D. dipsaci and its presence could have serious ramifications for NM’s alfalfa, onion, and garlic producers. 

In May of 2015 garlic plants (Allium sativum) from a home garden in were submitted to the Plant Diagnostic Clinic at NMSU.  The grower reported poor growth in ~30% of 1,200 plants originating from seed purchased in southern New Mexico.  Early symptoms included chlorosis, wilting, and poor root and bulb development.  As the disease progressed, roots turned brown, were easily separated from the bulb, and older foliage had collapsed and turned straw colored (Figure 1).  Microscopic examination showed large numbers of nematodes present in symptomatic garlic plants. Based morphological characteristics of the nematode and the DNA sequence of the ITS-1 region, the nematodes were identified as D. dipsaci.

This discovery is highly significant as this nematode has the potential to cause significant economic losses on agriculturally important hosts grown in the state and in the region. The longevity of this pest in the soil and international trade issues are major concerns for producers. Based on information from the grower it appears that this is an isolated introduction from infested plant material which can potentially be contained as the presence of D. dipsaci was discovered before any material was harvested or distributed. Monitoring of production areas in the state will be performed to determine if this was an isolated and contained introduction or if this important pest has become established in NM.
 
Stem and bulb nematode isolated from garlic
(photo: J. Beacham, NMSU)

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