Additional index words. AFLP, cluster analysis, genetic diversity, watermelon, germ plasm identifi cation Abstract. Amplifi ed fragment length poly mor phism (AFLP) analyses were used to as sess genetic diversity among 30 genotypes of watermelon [Citrullus lanatus (Thunb.) Mansf.] representing a broad genetic base, including breeding lines and commercial germ plasm. Eight AFLP primer com bi na tions se lect ed from 64 primer combinations were poly mor phic. The polymorphism was 13.0% to 31.9% within the 28 cultivars examined, and 45.3% to 64.2% among all the genotypes. Each genotype could be suc cess ful ly dis tin guished based on AFLP scor ing. Cluster grouping of accessions based on the AFLP analysis was consistent with that from classifi cation by pedigrees and ecotypes.

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Seven Solanum tuberosum ssp. tuberosum and three Solanum tuberosum ssp. andigena accessions were crossed to produce 12 Tuberosum × Tuberosum (T × T) and 9 Tuberosum × Andigena (T × A) progenies. These families were evaluated for five important traits for two successive clonal generations under short day sub-tropical plains. The differences in yield, average tuber weight and tuber number between T × T and T × A families in an early (75 days) crop were not significant. Compared to conventional intra-Tuberosum families, T × A families had significantly higher % tuber dry matter and specific gravity. In contrast to intra-Tuberosum crosses, T × A crosses exhibited a positive heterosis for tuber yield. Compared to T × T families, T × A families showed significantly higher heterosis for yield and tuber number. Comparison of T × T and T × A families and parents using canonical analysis led to the identification of superior hybrid families and superior parents. Some T × A progenies were close to breeding goal and thus can be used for selecting high-yielding cultivars. This revealed the usefulness of Andigena genotypes as parents in developing early bulking potato cultivars with broad genetic base for short day sub-tropical plains.

SUMMARYPedigree analysis was used to study the genetic background of 66 Indian early maturing potato selections, the pedigree of which was traced back to 35 ancestors. Six of the 35 contributed 0·42 of the genetic base, which shows the narrow genetic base of Indian early maturing genotypes. Genotypes 2814 (a)1 (f=0·145) and 3069 (d)4 (f=0·145) were the ancestors which appeared most frequently. Based on the coefficient of relationship, the 66 selections were grouped into seven groups with one common ancestor in almost all the selections within a group. The genotypes Kufri Ashoka, Kufri Pukhraj, AGB-69-1, Kufri Jyoti, Kufri Alankar, Kufri Lauvkar and Kufri Kuber were identified as very important parents/ancestors, carrying specific gene complexes valuable in new selections. Crosses between selections from different diversity groups can result in the selection of useful clones while increasing or maintaining genetic diversity, which is desirable to ensure sustainable breeding progress in the future.