Broad-sense heritability and stability of internal heat necrosis and specific gravity in tetraploid potatoes

Internal heat necrosis (IHN), a severe physiological disorder of potato (So lanum tuberosum L.) tubers, is characterized by brown spots or blotches tha t first appear toward the apical end of the tuber parenchyma but in severe cases may involve most of the parenchyma tissue. The purposes of this study were to determine the amount of genetic variation for and the stability of IHN in tetraploid potato clones, and the relationships among IHN, specific gravity, and tuber size distribution. Nineteen potato clones (four cultiva rs and 15 breeding selections) were grown in Bridgeton, NJ and Painter, VA from 1991 to 1993 in a randomized complete block with four replications of 20 hills per plot. The crop was harvested 2 to 3 wk later than normal harve st time to provide for maximal exposure to beat stress. All tubers were har vested and graded by size. All tubers >64 mm in diameter were quartered lon gitudinally and rated by size for MN (1 = severe IHN; 9 = no IHN). Incidenc e and severity of IHN were recorded. Broad-sense heritabilities and their 9 5% confidence intervals were: 0.83 (0.68, 0.93) for incidence of MN in Size 3 (64-83 mm diameter) tubers; 0.88 (0.71, 0.94) for incidence in Size 4 (> 83 mm diameter) tubers; 0.85 (0.72, 0.94) for severity of MN in Size 3 tube rs; 0.90 (0.78, 0.96) for severity of IHN in Size 4 tubers; 0.92 (0.85, 0.9 7) for specific gravity in Size 3 tubers; 0.77 (0.54, 0.91) for specific gr avity in Size 4 tubers; and 0.86 (0.73, 0.94) for total yield. Several of t he more IHN-susceptible clones were unstable for IHN both before and after environmental heterogeneity was removed. The correlation between incidence and severity of IHN was very high. There was no correlation between IHN and total yield or specific gravity. The results of this study indicate that b reeding high yielding, high specific gravity cultivars for resistance to IH N should be feasible.