Distribution and Socio-economic Impact of Blast Pathogen, Molecular Characterization of associated Fungi and Screening for Disease Tolerance in Kenyan Finger Millet (Eleusine coracana)

Abstract

Finger millet is an underutilized, climatic resilience grain crop with significant nutraceutical value and agricultural diversification prospects. Blast disease impedes its production and productivity causing a yield lose of 10-50% in Kenya. The disease is widely distributed and its impact occurs in all finger millet growing areas of Southern Asia and Eastern Africa. Sustainable finger millet blast management approaches in Kenya are threatened by inadequate farmers’ knowledge and poor blast management techniques used that eventually impact on their socio economic status. Besides, information on occurrence, severity and distribution of blast in Kenya is not well established.This is coupled with limited information on the genetic diversity of fungal species associated with the blast pathogen. This information forms a basis on which long term sustainable blast management approaches that meet farmers preferences can be laid. This study aimed at assessing farmers’ knowledge, practices and social economic effects of finger millet blast andthe disease occurrence, severity and distribution. The study further sought to characterize the genetic diversity of the fungal species associated with blast infected tissues, and screening for host tolerance of different varieties of Kenyan finger millet. Survey studies were done to assess farmers knowledge, practices and socio-economic impact on blast disease occurrence, distribution and severity. A semi-structured questionnaire, through face-to face interviews was administered to 325 farmers from five Counties in Kenya namely Bungoma, Busia, Kisii, Makueni and Machakos in 2018 and 2019. The data collected was analyzed using the SPSS statistical software version 25. Disease Occurrence was based on either presence or absence of infected plants in the field. Severity assessessment was based on an incidence score of low (0-29)=1, moderate (30-69%)=2 and very severe (>70%). Disease distribution was based on spatial disease spread on the farms. Plant tissues exhibiting blast disease symptoms were collected and placed in sterile bags for morphological and molecular characterization using internal transcribed spacer (ITS) and 28S rDNA regions. The blast pathogenic agent was then isolated and used for pathogenicity assays to observe the disease symptoms and effect of the pathogen on growth parameters such as plant height, leaf area index, chlorophyll a, chlorophyll b and carotenoid contents. This study showed that 90% of the farmers recognized blast disease as the greatest constraint to finger millet production with 51% of respondents reportinghigher severity in the dry season. Majority (72%) of farmers in Bungoma county were able to relate blast disease to the type of finger millet variety planted. Hand weeding was perceived as the most effective blast management practice by 99% of the respondents although it was identified as a very laborious task. Additional management practices chosen by 60% of respondents included ash treatment, uprooting infected plants, and herbicide application once a season. A conclusion was drawn that farmers in all the counties surveyed have limited knowledge on blast disease and the management practices used are basic. Blast disease occurred in all the counties visited with Machakos (56%) having the least leaf blast severity while Busia county (82%) had the highest disease severity in all the plant parts (leaf,neck and finger). Fifty five isolates were obtained from finger, leaf and neck with a total of 11 genera for 28SrDNA and 10 together with two unnamed fungi for ITS. Phylogenetic studies revealed two trees with similar topologies for both regions and the isolates were assigned to three classes of Phylum Ascomycota, namely Eurotiomycetes, Dothiodeomycetes and Sordariomycetes. There was a significant difference (p≤ 0.05) in varietal difference in leaf area index, plant height and photosynthetic pigments contents in presence of both pathogens. Genotype GBK 043050 (GBK 42) had a disease severity score of 3.6 and 3 in presence of C. lunata and P.oryzae respectively that was equivalent to a disease reaction of moderately susceptible. GBK 043050 (GBK 42) and Engundi varieties were not significantly different at (p≤ 0.05).Thus, the two varieties were deemed to be tolerant to both pathogens. In conclussion, the study recommends a concerted d focus on improving farmers' adoption of best blast management practices, identifying the possible role played by fungal species associated with blast infected plant tissues during finger millet blast pathogenesis, and developing blast-tolerant finger millet varieties with farmer preferential traits. It is recommended that capacity building be done for all farmers from all the Counties surveyed.