Assessing morpho-chemical and genetic diversity in acid limes germplasm using microsatellite markers

Acid limes are highly nutraceutical and have great market demand. In Pakistan, two lime varieties are cultivated including ‘Mexican lime’ and ‘Eustis limequat’. Hence, other potential varieties were characterized for morphogenetic variability. Leaf shape was elliptic in ‘Mexican lime’ and ‘Eustis limequat’ and obcordate in ‘Tahiti lime’, ‘Seedless lime’ and ‘Tavares limequat’ while the leaf area was greater in ‘Seedless lime’. ‘Tavares limequat’ developed the heaviest fruit (74.55 g) with greater fruit length while fruit diameter was higher in ‘Seedless lime’. Juice weight and juice percentage were greater in ‘Tavares limequat’ and ‘Seedless lime’ respectively. ‘Tahiti lime’, ‘Seedless lime’ and ‘Tavares limequat’ were found as a seedless variety. Titratable acidity was higher in ‘Eustis limequat’ while sugar to acid ratio was lower in ‘Eustis limequat’, ‘Mexican lime’ and ‘Seedless lime’ varieties. Simple sequence repeat (SSR) markers analysis revealed great genetic diversity among populations. Maximum alleles (9-11) were amplified by using CAC23 and CTT01 markers which showed higher discrimination and heterozygosity. CAC23 and CTT01 markers effectively amplified three alleles in triploids (‘Tahiti lime’ and ‘Seedless lime’), a single allele in diploids (‘Mexican lime’, ‘Eustis limequat’) and two alleles, including a unique allele in diploid ‘Tavares limequat’. Cluster analysis bunched closely related genotypes into two groups, STRUCTURE analysis confirmed the admixture nature of all genotypes and ‘Tavares limequat’ was found to be the most divergent. Conclusively, selected SSR markers effectively discriminated among diploid and polyploid acid limes and may be extended to other citrus species as well. These findings could be helpful for the selection and conservation of heterozygous material and utilization in breeding and germplasm enhancement programs.