Plantlets and Micro-Rhizome Regeneration, Genetic Diversity and Evaluation of Ginger (Zingiber Officinale Roscoe) for Bacterial Wilt in Ethiopia
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Date
2024-06
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Addis Ababa University
Abstract
Ginger (Zingiber Officinale Roscoe) is an important crop used for many purposes and is a major spice across Ethiopia since 13th century. Ginger production, productivity, and product quality were limited due to different biotic and abiotic factors. Among the biotic factors, it was challenged primarily due to bacterial wilt disease eruption in the last decade. The use of clean tissue culture generated seed rhizome as part of integrated management with other cultural practices was an option to reduce the disease pressure. However, the disease still poses a threat to ginger cultivation in the country. In the absence of efficient strategies to reduce the disease impact, the use of tolerant cultivars appears to be the best disease control strategy. Hence, this study aimed to enhance disease-free planting materials generation and ginger diversity analysis. The first and second experiments targeted in vitro disease-free plantlets generations and micro-rhizome induction respectively. Experiments three, and four are with the objectives of genetic diversity assessment among ginger accessions using morphological and molecular markers consecutively. The last objective of the study focused on evaluating the study materials for resistance against the pathogen. In the course of in vitro regeneration, alternative nitrogen source salts replaced 1.65 g/l ammonium nitrate in Murashige and Skoog medium. xvi Ammonium chloride at 1.0 g/l, potassium nitrate (3.8 g/l), and urea (3.0 g/l) are the best alternatives. Micro-rhizome induction resulted in viable in vitro generated micro-rhizomes that are planted directly in the soil. Murashige and Skoog medium supplied with elevated levels of sucrose (80 g/l) and benzyl amino purine (6.0 mg/l) was the best treatment among thirteen treatment combinations for the micro-rhizome induction. For genetic diversity analysis, both by morphological traits and SSR markers, 100 ginger accessions including two released varieties (Boziab and Yali) and wild species (mango ginger) were collected from different agro-ecologies of south, central, and southwestern parts of Ethiopia. The morphological trait-based analysis was done by using 24 quantitative and qualitative traits. The analysis has revealed the availability of genetic diversity via high values of genetic coefficient of variation, heritability, and genetic advance as mean. Cluster analysis also grouped the 100 accessions into four clusters. The study materials assigned to four sub populations; Southern, Central, Southwest and Oromia based on the area of the collection were also assessed for genetic diversity using twelve polymorphic SSR markers. The SSR based molecular diversity population structure anlysis has grouped the 100 accessions into three clusters unlike morphological-based analysis which resulted in four clusters. AMOVA has showed 96% among individuals and 4% variation was among the four populations. Sprouted buds were found better for quality DNA extraction in ginger, which is the first of its kind. In both morphological and SSR-based diversity analysis, the wild type (JW89) was unique due to some traits like rhizome size and unique fragment bands. The diversity analysis based on morphological traits and SSR markers, in general, revealed that there is high genetic diversity among ginger accessions. Evaluation of the 100 study materials against bacterial wilt disease pathogen under the protected conditions in the screen house and further tested in the field also revealed that there is response variation among the accessions. Disease severity, disease incidence, days to severe disease symptoms, fresh and dry yield losses showed high variations among accessions. the evaluation experiment revealed that (12) accessions were grouped as very tolerant accessions. The majority, 88 accessions also showed different response levels from tolerant to very susceptible based on disease scores and yield loss analysis results. Four accessions (BASP19, BSSB47, BSSB49, and OKW63) and wild type (JW89) have shown consistent variations being grouped to very tolerant in disease screening, in similar clusters during morphological and molecular genetic diversity analysis. The study results of the three separate experiments' morphological traits, SSR markers, and screening against pathogen gave clue that there might be potential markers linked to disease tolerance and high rhizome yield, which needs further verification.
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Keywords
Ammonium Nitrate, Disease Free, Markers, Plantlets, Diversity, Ginger, Micro-Rhizome, Tolerance, Sucrose, Sprouts