FOLIAR HEAT TOLERANCE OF 2 HYBRID HOLLIES

Temperatures producing heat damage in leaves of Ilexxmeserveae S.Y. Hu 'Blue Prince' and Ilex rugosa X cornuta Lindl. & Paxt. 'Mesdob' (Chin a Boy) were evaluated using electrolyte leakage and chlorophyll fluore scence techniques. Whole leaves were exposed to temperatures from 30 t o 65C for 30 minutes to determine critical midpoint heat-killing tempe ratures (T(m)) using electrolyte leakage techniques. The T(m) for 'Blu e Prince' and 'Mesdob' was 52.4 +/- 0.1C and 53.8 +/- 0.1C, respective ly. Dark-adapted leaves were heated for 30 minutes in darkness at temp eratures between 30 and 57C before chlorophyll fluorescence was measur ed. Initial (F.) and peak fluorescence measurements were higher at 54 and 55C for 'Mesdob' than for 'Blue Prince'. Cultivar had no effect on variable fluorescence (F(v)). Based on the F(v):F(o) ratio, 'Mesdob' was estimated to have a higher optimal plant growth temperature than ' Blue Prince'. The physiologic data support the hypothesis that L cornu ta as a parent conferred heat tolerance to the interspecific hybrid in this study.