Guava SSR Analysis: Diversity Assessment in US and Similarity to Accessions Associated with Reducing Citrus Huanglongbing in Vietnam

Closely interplanting citrus (Citrus sp. L) and guava (Psidium guajava L.), in Vietnam were reported to greatly slow progression of huanglongbing (HLB). It was hypothesized that volatiles in the guava may repel the Asian citrus psyllid (ACP, Diaphorina citri Kuwayama) which vectors the HLB causal bacterial agent. To date, field confirmation of ACP being repelled by guava has not been demonstrated in the U.S., but it was not known whether the guava selections used were the same as those reported to be effective in Vietnam. In this study, SSR (simple sequence repeat) analysis was conducted on all readily accessible U.S. guava accessions, as well as material from three Vietnamese citrus/guava orchards, to determine whether Vietnamese guava genotypes reported to suppress ACP were already available in the U.S. and to assess diversity of guava available in the U.S. Accessions included 60 distinct sources, and multiple samples were collected from 10 of these as an internal check. Ten SSR primer pairs were used in the analysis. Alleles per locus ranged from 4 to 8, with an average of 6.2. Forty different genotypes were identified, as several accessions appeared to be synonymous based on this analysis. The cluster analysis using the neighbor-joining method revealed five distinct affinities. The Vietnamese accessions were placed in two of the five major clusters. Several guava varieties in Florida are in the same clusters as the Vietnamese cultivars. However, the sweet pink-fleshed varieties that have predominated in the western hemisphere did not cluster with the accessions from Vietnam.