AFLP data suggest a potential role for the low genetic diversity of acid lime (Citrus aurantifolia Swingle) in Oman in the outbreak of witches' broom disease of lime

Acid lime (Citrus aurantifolia) is the fourth largest fruit crop in terms of cultivated area and production in Oman. However, over half a million lime trees were lost in Oman over the past 35 years due to witches' broom disease of lime (WBDL) which is caused by Candidatus phytoplasma aurantifolia. This study was conducted to examine genetic diversity of acid lime in Oman. AFLP analysis of 143 acid lime samples from Oman, 2 from Brazil and one from Pakistan using 4 primer pair combinations produced 980 polymorphic loci (100 %) and 146 AFLP genotypes. Despite the long history of acid lime cultivation in Oman, populations of lime from different districts were found to have low levels of genetic diversity (0.0888-0.2284). AMOVA analysis indicated the existence of high level of genetic differentiation (F_ST = 0.271) among populations of acid lime from Oman and Brazil, which indicates that both populations have evolved independently for a considerably long period of time. On the other hand, AMOVA analysis showed that only 11 % of the genetic variation exists among populations from the 18 different districts in Oman. This suggests frequent exchange of acid lime planting material across geographical regions in Oman. Findings from this study suggest that the low level of genetic diversity of acid lime in Oman and frequent movement of acid lime planting material across districts are two main factors which contributed to the rapid spread and high susceptibility of acid limes to WBDL in the country.