Variability analysis of improved sweet potatoes [Ipomoea batatas (L.) Lam] varieties in the Philippines

Genetic diversity is considered as man's best protection against food insecurity since it makes available the characters that could counteract threats to food production such as pest and adverse environmental conditions. However, genetic diversity in crops could decrease and even be lost by the replacement of landraces or native varieties which have high variability with those developed through breeding. In sweet potato, active breeding programs have been pursued by several research institutions in the Philippines in the last 30 years, resulting in 29 varieties approved for commercial production by the National Seed Industry Council (NSIC, formerly the Philippine Seed Board) as of 2005. These varieties yield at least twice higher than the traditional ones and will, thus, definitely increase sweet potato production in the country if these varieties are grown. The study analyzed the variability in 23 of the improved sweet potato varieties in the Philippines to determine if replacement of landraces by modern sweet potato varieties would be a threat to the existing genetic variation in the crop in the country. Variability was measured on the basis of 31 characters, 26 of which were qualitative. High diversity/variability was shown by the 23 varieties in 23 of 26 qualitative traits and all five quantitative characters in terms of the number of phenotypic classes exhibited as well as the values of the Shannon-Weaver diversity index, which averaged 0.70. The average Gower Similarity coefficients among variables were low, especially if only qualitative or highly genetically controlled traits were considered, an average of 0.37 among the 23 varieties and 0.28 among the three more popular ones. Thus, even if these modern varieties were planted in most of the sweet potato growing areas in the country, sufficient variability in the crop will still exist, at leased based on the characters studied. A more complete assessment of genetic diversity in the Philippine modern sweet potato cultivars by using other methods of variability is therefore recommended.