Evaluation of African tomato landraces based on morphological and horticultural traits
1. Introduction
Despite significant improvements, tomato production still faces major setbacks. According to Maerere et al., some biotic and abiotic factors are attributed to low yields and increased production costs. In terms of pest control, farmers overuse pesticide products, using pesticides more than 40 times per season in some tomato fields.
The low diversity of commercial tomato varieties has been identified as one of the main factors contributing to the susceptibility of crops to biotic and abiotic restrictions.
Crop landraces are widely used in breeding and have long been recognized as having valuable traits lost in cultivars, and the use of these traits has increased research results and understanding of genetic variation, thus promoting wider geo-adaptive breeding.
In Africa, a large number of tomato landraces are stored in gene banks with largely undocumented phenotypic and genotypic characteristics. Understanding this diversity is important for broadening the genetic resource base of tomato crops.
The current study aims to assess and document the extent of phenotypic diversity in African tomato landraces.
2. Materials and methods
The study was conducted at the Upper Kabete Field Station at the University of Nairobi in Kenya during short and long rains in 2014 and 2015, respectively.
The site is located at an altitude of 1940 meters, latitude between 10⁰140 200 s and 10⁰150 150 N, longitude between 360⁰440E and 360⁰450E, with an average annual rainfall of 1000 mm. Long rain lasts from March to December. The average monthly maximum and minimum temperatures are 23°C and 12°C, respectively.
The site soil is reddish-brown clay covered with dark and red clay, which belongs to humus nitrote, deep fertile, well-drained, thick surface soil, and has a block structure, which is conducive to the penetration and development of the root system; The clay mineral is mainly kaolinite.
The quantitative traits were: single leaf area, soil plant analysis and development, flowering to 50% days, ripening days, number of fruits per plant, fruit length, fruit width, and fruit weight per plant. Flowering days are recorded as the number of days from sow to flowering of 50% of the plants in each plot.
SPAD values of the flower formation stage were determined on the fully expanded young leaves of 3 plants in each stand and their average value was taken. This value is used with a non-destructive handheld chlorophyll meter at flowering.
Record the fruit length from the stem end to the flower end, and the fruit width at the maximum diameter of the cross-sectional fruit. The total number of fruits per plant was determined when physiological maturity, and the total weight of each fruit was determined by weighing method.
3. Results
Cluster analysis identified two main clusters (Cluster I and Cluster II), as shown in Figure 1. Cluster I has 63 accesses, divided into 7 subclusters, while Cluster II has only 6 accesses from Madagascar.
The member stems of Cluster I and Cluster II are purple and green, respectively. Subgroup "A" has 17 joins, most of them from South Africa and Madagascar. The subcluster "b" is dominated by South African and Moroccan species, and the subcluster "c" is dominated by Ethiopian species.
Subclusters have the fewest number of accesses. Subclusters " d " and " g " have members from different origins, while members from Morocco and Kenya dominate subclusters " e " and " f " , respectively.
The first 5 components of PCA explain 78.4% of the total variation, with the first 2 components contributing 40.7% (Figure 1). PCA identified 6 personality traits including green shoulder, fruit size, fruit appearance color, short pubescent density, flower color and fruit cross-sectional shape, which were the main traits that positively contributed to PC1. Compared with other traits, green shoulder (0.414) and fruit size (0.336) contributed more to this PC.
The load of leaf density, growth type, stem color and fruit shape on this component was -0.478, -0.445, -0.406 and -0.091, respectively.
4. Discussion
From the treemap, it is not possible to classify all tomato material from the same collection site or site into a specific group, but it is clear that most of the research material is fairly relevant. It is also possible that farmers' constant recycling of tomato seeds and selection leading to large-scale separation has led to widespread phenotypic variation in tomato crops.
However, the color of the stems clearly divides these plants into two broad categories, purple stems and green stems.
The variation observed in this study provides a potential source of genetic diversity for tomato crop improvement. Most of the traits between the various plasmas in the same area have high similarity. This indicates avoiding materials with similar genetic backgrounds, as well as avoiding materials with the least correlated traits.
4. References
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[4] Islam, B.M.Ivy, N.A.Rasul, M.G.Zakaria, M. 2010. Genetic trait association and pathway analysis of exotic tomato genotype. Bangladesh J. Plant Varieties.Genoa.23,13-18.
