Abstract
Two-hundred and twenty-six old avocado trees (Persea americana Mill) derived from seeds were selected from eight districts of the Mbeya, Njombe and Songwe regions in Tanzania. The tree, leaf, fruit and seed characteristics were studied using the descriptors for avocado (Persea spp.) from the International Plant Genetic Resources Institute. Cross tabulation and Chi-square tests were conducted in order to assess the distribution of traits between districts and altitude ranges. Principle coordinate analysis (PCoA) and hierarchical cluster analysis (HCA) were used to assess variation of traits within and among districts. Various morphological features were observed among the samples which point to the existence of the Mexican, Guatemalan and West Indian avocado races in Tanzania. The biplot from PCoA revealed extensive variation between the sampled trees at the district level but no clear groupings of the samples based on geographic location. Likewise, dendrograms ensuing from the neighbor–joining and Wards methods displayed that the avocado samples from the same district and even region differed considerably. This morphological trait variation suggests high diversity that may help in planning germplasm management and conservation, as well as breeding strategies in the future.
Highlights
Avocado (Persea americana Mill) is an important plant from the family Lauraceae bearing fruits that are highly appreciated for their nutrition and health benefits [1,2]
In Mbeya rural, 50% of the avocado trees were found at altitude range of 1861 to 1908 masl, while others were found at altitudes that were as low as 1794 and as high as 1934 masl with exclusion of outliers whose lowest and highest values were 1534 and 2136 masl, respectively
For the Wanging’ombe avocado trees, 50% of them were found at altitude range of 1882 to 1954 masl, while others were at altitudes that were as low as 1860 and as high as 2007 masl
Summary
Avocado (Persea americana Mill) is an important plant from the family Lauraceae bearing fruits that are highly appreciated for their nutrition and health benefits [1,2]. The avocado tree may grow as high as 20 m, while its trunk can reach 90 cm in diameter and the leaf can grow up to 40 cm long [3,4]. The fruits can be 7 to 20 cm long and up to 15 cm wide, weighing 100 to 1000 g [3]. The peel may be reddish purple, deep-green, yellowish green or dark purple and sometimes speckled with yellow dots, while its thickness can measure from less than one millimetre up to 6 mm [3]. Avocado flesh can be completely pale to rich-yellow in colour, buttery, bland or nutlike in taste [3]. The seed may have shapes like roundish, conical, oblate or ovoid. The fruit may lack seed due to the absence of pollination [3,4]
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