ARS | Publication request: First report of root rot of lentil caused by Aphanomyces euteiches in Idaho

Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: February 6, 2010
Publication Date: April 1, 2010
Citation: Vandemark, G.J., Porter, L. 2010. First report of root rot of lentil caused by Aphanomyces euteiches in Idaho. Plant Disease. 94:480.

Interpretive Summary: Lentils are an important component of cropping systems in the Pacific Northwest and North Central US. They are typically grown in rotation with small grains such as wheat and barley, and confer several benefits to small grain production, including breaking disease cycles and, through an association between lentil roots and soil bacteria, producing nitrogen that can be used as fertilizer in the subsequent grain crops. Lentils in themselves are very nutritious, having a high content of protein and antioxidant compounds, and are largely exported to other nations, which helps reduce trade deficits and contributes positively to rural communities in which lentils are produced. Very little is known about diseases of lentils, but a lack of resistance to specific diseases likely results in considerable production losses. Recently, we observed lentil plants growing in a production field in ID that exhibited several symptoms of disease, including stunting, root rot, and yellowing and reddening of leaf surfaces. These plants were collected and fungi and fungi-like organisms were isolated from the roots of these plants. Using molecular techniques that screen DNA for the presence of specific genetic markers, we determined that one of the organisms isolated from diseased lentil roots was the water mold Aphanomyces euteiches. A. euteiches is known to be the cause of the most globally destructive root rot disease of dry pea. We screened 33 advanced lentil breeding lines and three commercial varieties of lentil (Pardina, Eston, and Crimson) for resistance to A. euteiches using a greenhouse protocol that is commonly employed to screen peas for resistance to Aphanomyces root rot. All of the lentils tested were at least moderately susceptible to the pathogen, and most of the lentil lines were highly susceptible. Most lentils in the Pacific Northwest are grown on land that has been historically used to cultivate peas, which are highly susceptible to A. euteiches. The pathogen produces a survival spore that can live in the soil for up to 10 years, and it is probable that the pathogen we isolated originally infected peas. Our results suggest that resistance to A. euteiches is lacking in the majority of elite, high yielding lentil breeding lines and varieties. We will use the techniques we have developed in this study to screen more advanced lentil breeding lines, along with a large sample of preliminary breeding lines and a group of lentil samples that represent the global diversity within lentil, to identify sources of resistance to Aphanomyces root rot. Once resistant materials are identified, they will be used as parents to make crosses that will result in the development of high yielding lentil varieties that are resistant to Aphanomyces root rot. This will improve lentil production and increase the sustainability of grain cropping systems in the US.

Technical Abstract: In June 2008, apparently diseased lentil plants (Lens culinaris L. cv. Crimson) were observed in a production field in Kendrick, ID. Symptoms included stunting, leaf chlorosis, reddening of abaxial leaf surfaces, browning of entire root systems and root necrosis. Roots of symptomatic plants were surface sterilized, plated on water agar plates, and pure cultures were obtained by subculturing hyphal tips. Several cultures exhibited white, moderately branched mycelia characteristic of Aphanomyces euteiches. DNA was extracted from mycelia and subjected to PCR using primers that amplify a 1332 bp sequence characterized amplified region that is specific for A. euteiches. DNA from A. euteiches isolated from pea (Pisum sativum L.) was used as a positive control for PCR. A PCR product of the expected size was amplified from the positive control and also from a single isolate obtained from symptomatic lentils. Zoospores of the isolate were produced and used to screen 33 advanced lentil breeding lines and 3 lentil cultivars (Eston, Crimson, and Pardina). One week after emergence, all seedlings were inoculated with either 20,000 or 5,000 zoospores of A. euteiches isolated from lentil. Plants were scored 14 d after inoculation using a 0 (no symptoms) to 5 (dead plant) disease severity index (DSI) that is commonly used to evaluate disease reaction to A. euteiches in pea. For each inoculum level, six plants of each lentil genotype were scored for disease reaction, and the experiments were repeated once. All lentil breeding lines and cultivars were at least moderately susceptible to A. euteiches (mean DSI = 3) at both inoculum levels, and the majority was highly susceptible (DSI = 4). The results of these preliminary screenings suggests that resistance to A. euteiches is severely lacking in elite, high yielding lines and cultivars of at least three major market classes of lentils (Eston, Turkish Red and Pardina). In the major production areas of ID and WA, lentils are commonly grown on land that has historically been used to cultivate dry peas, which suffer severe loss potential due to A. euteiches. Additional screening of preliminary lentil breeding lines and Plant Introduction (PI) accessions is being conducted to identify sources of tolerance to A. euteiches in lentil.