A Specific and Sensitive Method for the Detection of Colletotrichum lindemuthianum in Dry Bean Tissue

Hyperspectral imaging for the detection of plant pathogens in seeds: recent developments and challenges

Food security, a critical concern amid global population growth, faces challenges in sustainable agricultural production due to significant yield losses caused by plant diseases, with a multitude of them caused by seedborne plant pathogen. With the expansion of the international seed market with global movement of this propagative plant material, and considering that about 90% of economically important crops grown from seeds, seed pathology emerged as an important discipline. Seed health testing is presently part of quality analysis and carried out by seed enterprises and governmental institutions looking forward to exclude a new pathogen in a country or site. The development of seedborne pathogens detection methods has been following the plant pathogen detection and diagnosis advances, from the use of cultivation on semi-selective media, to antibodies and DNA-based techniques. Hyperspectral imaging (HSI) associated with artificial intelligence can be considered the new frontier for seedborne pathogen detection with high accuracy in discriminating infected from healthy seeds. The development of the process consists of standardization of methods and protocols with the validation of spectral signatures for presence and incidence of contamined seeds. Concurrently, epidemiological studies correlating this information with disease outbreaks would help in determining the acceptable thresholds of seed contamination. Despite the high costs of equipment and the necessity for interdisciplinary collaboration, it is anticipated that health seed certifying programs and seed suppliers will benefit from the adoption of HSI techniques in the near future.

Dry Bean and Anthracnose Development From Seeds With Varying Symptom Severity

Anthracnose, caused by the fungal pathogen Colletotrichum lindemuthianum, is a damaging seed-transmitted disease of dry beans that causes reduced seed quality and yield. Seed-to-seedling transmission of C. lindemuthianum has been documented as high as 15% in asymptomatic seeds under greenhouse conditions. Increasing pathogen colonization in seeds has been correlated with increasing anthracnose seed symptoms via quantitative PCR (qPCR), but stem colonization has not been quantified. Previous studies also have characterized seed yield and quality losses caused by planting C. lindemuthianum-infected seeds, but none evaluated the effect of growing asymptomatic seeds on disease and plant development under field conditions. A real-time qPCR assay was developed in this study and used to detect C. lindemuthianum in the stems of seedlings as early as 15 days after planting. Field trials measured the seed-to-seedling transmission of C. lindemuthianum across levels of anthracnose symptoms in seeds ranging from healthy to severely discolored. Results from these two field trials indicated that emergence and yield decreased and foliar symptoms, pathogen detection, and incidence of symptoms on progeny seeds increased as the severity of infection in planted seeds increased. In both years, planting asymptomatic seeds resulted in higher anthracnose severity than planting healthy seeds. Yield, seed weight, and incidence of symptoms on progeny seeds were not higher in asymptomatic seeds than in healthy seeds in 2014, when moderate disease pressure was observed. However, these factors were significantly different in 2015, when anthracnose severity was driven up to 75% by conducive weather conditions. This serves as a strong warning to growers that planting seed grown in a field where anthracnose was present, even if those seeds are asymptomatic, can result in yield and quality losses. Planting certified dry bean seed is always recommended.

The Colletotrichum destructivum species complex - hemibiotrophic pathogens of forage and field crops

Colletotrichum destructivum is an important plant pathogen, mainly of forage and grain legumes including clover, alfalfa, cowpea and lentil, but has also been reported as an anthracnose pathogen of many other plants worldwide. Several Colletotrichum isolates, previously reported as closely related to C. destructivum, are known to establish hemibiotrophic infections in different hosts. The inconsistent application of names to those isolates based on outdated species concepts has caused much taxonomic confusion, particularly in the plant pathology literature. A multilocus DNA sequence analysis (ITS, GAPDH, CHS-1, HIS3, ACT, TUB2) of 83 isolates of C. destructivum and related species revealed 16 clades that are recognised as separate species in the C. destructivum complex, which includes C. destructivum, C. fuscum, C. higginsianum, C. lini and C. tabacum. Each of these species is lecto-, epi- or neotypified in this study. Additionally, eight species, namely C. americae-borealis, C. antirrhinicola, C. bryoniicola, C. lentis, C. ocimi, C. pisicola, C. utrechtense and C. vignae are newly described.

Genetic Diversity and Aggressiveness of Fusarium spp. Isolated from Canola in Alberta, Canada

Canola (Brassica napus) is one of the most economically important oilseed crops in Canada. Fusarium seedling blight is a root disease with the potential to cause severe yield reductions in canola. Fusarium spp. are commonly isolated root pathogens from fields in Alberta. Fusarium infection can also cause root rot in adult plants. In this study, 128 isolates identified as Fusarium spp. were recovered from field soils in central Alberta and from the roots of diseased canola plants with typical Fusarium seedling blight symptoms. Six species of Fusarium were identified, with Fusarium acuminatum as the predominant species (57 of 128 isolates, 44.5%). Phylogenetic analyses based on the translation elongation factor 1-α and the internal transcribed spacer sequence data were used for evaluation of genetic variations, and also used for Fusarium spp. identification in combination with morphological characteristics and polymerase chain reaction-based analyses. Based on disease ratings in pathogenicity tests, six isolates of F. avenaceum showed high aggressiveness on canola. Also, the aggressiveness varied within all Fusarium spp. No correlation was observed between aggressiveness and the geographic origin of the isolates.