Morphological and genetic diversity of Mexican guava germplasm Sanjuana Herna ´ndez-Delgado 1,3 , Jose ´ Sau ´l Padilla-Ramı ´rez 2 , Alejandro Nava-Cedillo 1 and Netzahualcoyotl Mayek-Pe ´rez 3 * 1 Instituto Tecnolo ´gico Agropecuario de Aguascalientes (ITA 20), Km 18 Carretera Aguascalientes-San Luis Potosı ´, El Llano, 20330, Aguascalientes, Me ´xico, 2 Campo Experimental Pabello ´n, Instituto Nacional de Investigaciones Forestales, Agrı ´colas y Pecuarias (INIFAP), Apartado Postal 20, Pabello ´ n de Arteaga, 20660, Aguascalientes, Me ´xico and 3 Centro de Biotecnologı ´a Geno ´mica-Instituto Polite ´cnico Nacional. Blvd. Del Maestro esq. Elı ´as Pin ˜ a s/n, Col. Narciso Mendoza, 87100, Reynosa, Me ´xico Received 18 November 2005; Accepted 11 October 2006 Abstract Fifty morphological characteristics, fruit production over 3 years (from 1999 to 2002) and the amplified fragment length polymorphism (AFLP) technique were used to analyse a set of 48 guava (Psidium guajava L.) accessions cultivated in Mexico, in order to characterize their gen- etic relationships. Germplasm was collected from the Calvillo-Can ˜ones region and planted in Huanusco, Mexico. The study included two P. cattleianum (Sabine) and two P. friedrichstha- lianum (Berg-Niedenzu) accessions from Costa Rica as outgroups. Principal component anal- ysis (PCA) explained less than 30% of total variation and 14 characteristics from trees (1), leaves (2) and fruits (11) were the most informative. PCA analysis separated the germplasm into three major groups of accessions based on fruit size and weight, stem diameter and leaf size. Signifi- cant differences in fruit yield were detected among accessions and years, where P . guajava produced 36 kg/year/tree of fresh fruit while P. cattleianum and P. friedrichsthalianum showed fruit yield lower than 7 kg/year/tree. The fruit yield broad sense heritability was 0.25. The AFLP analysis produced two clusters of Psidium accessions, the first included P. cat- tleianum and P. friedrichsthalianum, and the second P. guajava accessions. This is the first report about the use of AFLP marker methodology for the genetic characterization of Mexican native guava germplasm and the results based on phenotypic and productive characteristics suggest that germplasm was selected from open pollinated trees. Keywords: AFLP analysis; fruit yield; morphology; Psidium cattleianum; Psidium friedrichsthalianum; Psidium guajava L. Introduction Mexico is the second largest guava producer worldwide (around 27,000 ha being cultivated), just behind India. More than 50% of guavas are cultivated in the ‘Calvillo- Can ˜ones’ region of Me ´xico (Gonza ´lez-Gaona et al., 2002), which includes the states of Aguascalientes (Calvillo) and Zacatecas (Tabasco, Huanusco, Jalpa, Apozol and Juchipila). The guavas from this region exhibit the highest quality and longest shelf-life (Padilla-Ramı ´rez et al., 2002). Fruit yields in the Calvillo-Can ˜ones region range from 13 to 15 ton/ha and are generally limited by low water levels, soil salinity and fertility, amongst other abiotic (drought, frost) and biotic (nematodes, insect pests and diseases) factors (Gonza ´lez-Gaona et al., 2002). Guava breeding could help increase crop productivity *Corresponding author. E-mail: nmayek@ipn.mx q NIAB 2007 ISSN 1479-2621 Plant Genetic Resources: Characterization and Utilization 5(3); 131–141 DOI: 10.1017/S1479262107827055