Lentil anthracnose: epidemiology, fungicide decision support system, resistance and pathogen races

Abstract

Colletotrichum lentis causes anthracnose of lentil (Lens culinaris) in Canada that results in defoliation, stem girdling and severe yield losses, but the disease is rarely reported elsewhere. The pathogen survives as microsclerotia on lentil debris for up to 3 years when buried in the soil, but loses viability on the soil surface. Windborne debris spreads the pathogen to neighbouring fields, while seedborne infection is less important. Foliar fungicides were registered, and a fungicide decision support system was developed which assessed disease risk with 85% accuracy. Around 2300 L. culinaris accessions from 50 countries were screened for resistance. Congruently, two races-Ct1 and Ct0were identified on differential lentil lines. Resistant lines were generated by cycles of inoculation and selfing of single resistant plants which resulted in the following three accessions resistant to both races: VIR2633 (Georgia), VIR2058 and VIR2076 (Czech Republic), while six and 49 lines had resistance to Ct0 and Ct1, respectively. Ct1 resistance is controlled by recessive and dominant genes crt1 and CtR3 in variety 'Indianhead', ctr2 and CtR5 in accession PI345629 and CtR4 in PI320937. Molecular markers linked to Ct1 resistance were identified on linkage group six, close to Ascochyta lentis resistance, and were used to combine resistance to both pathogens in breeding lines. Two repeat rich regions in the intergenic spacer (IGS) of ribosomal DNA can be used to differentiate the two C. lentis races. Utilizing length polymorphisms in a 39 nucleotide repeat region showed the races were equally frequent among isolates collected between 1991 and 1999, while 95% belonged to race Ct0 in 2010, likely because lentil varieties are susceptible to race Ct0, but around one-third of the varieties had Ct1 resistance.

Minimizing Lentil Harvest Loss through Improved Agronomic Practices in Sustainable Agro-Systems

“…Fungicide and herbicide applications are commonly used in lentil fields to prevent the outbreak of fungal disease and weeds [12,14]. Usually, pesticide efficacy depends on the types of applied chemicals, application timing, seeding rates, crop cultivars, and environmental conditions [13,14].…”

“…The unique morphological structure of lentil plants, combined with hot and wet micro-climate created by the rolling practice and stubble management, often make lentil plants vulnerable to fungal disease and weed competition. Lentils are one of the least competitive legume crops and are susceptible to various fungal diseases that can lead to severe defoliation, plant girdling, and yield loss [12,13]. Lentils also often suffer yield loss due to their short stem, small canopy, and slow canopy establishment [14].…”

“…To counter the effects of disease and weed pressure, producers have relied on fungicide and herbicide applications in order to increase lentil yield. A number of studies have looked at pesticide types, application timing, and their interactions with different lentil cultivars [12,14,15]. However, there is little understanding of how essential pesticide applications in lentils influence plant morphological structure and yield, and whether they can interfere with physical agronomic practices, such as land rolling and stubble management.…”

Lack of effective resistance to the virulent race of Colletotrichum lentis in Lens culinaris Medikus subsp. culinaris

“…Race 1 is a less virulent race to which partial resistance was found in a number of L. culinaris subsp. culinaris accessions (Buchwaldt et al ., 2004, 2018). Resistance to this race was effectively transferred into elite lentil breeding lines and resulted in the release of a number of cultivars with partial resistance to race 1 in lentil production (Vandenberg et al ., 2002, 2006; Government of Saskatchewan, 2019).…”

Resistance to Anthracnose (Colletotrichum lentis, Race 0) in Lens spp. Germplasm

“…Then, it was renamed as C. lentis Damm based on (i) its host specialization on Lens and Vicia species [3]; (ii) the morphology of the conidium and (iii) the sequence of ITS (internal-transcribed-spacer) region of ribosomal DNA [4][5][6]. During the last decade, anthracnose has turned into one of the most damaging lentil diseases in countries such as Canada and USA [6][7][8]. Yield losses up to 70% on susceptible lines can easily occur under high disease pressure, favorable climatic conditions and absence of chemical control [9].…”