Maize (Zea mays ssp. mays) and eastern gamagrass (Tripsacum dactyloides) are known for their susceptibility to chilling injuries. Their hybrid (Z. mays T. dactyloides) showed higher tolerance to low temperatures (-2 °C) in the field than its parents. Exposure to 5 °C for 2 or 3 d reduced the variable to maximal chlorophyll fluorescence ratio (F V /F M ), an indicator of the maximum photochemical efficiency of the photosystem 2, and the variable to minimal fluorescence ratio (F V /F 0 ) more in maize and eastern gamagrass than in hybrid plants. Chlorophyll contents for rewarming plants (25 °C for 3 d) were lower than before chilling in both parents while values for hybrid plants were similar. Electrolyte leakage was higher in chilled than control plants but it did not show significant differences among genotypes. Our data suggest that hybrid plants have higher capacity to recover from chilling injury in controlled conditions than their parents.

Since corn has been classified as one of the most sensitive crops to soil salinity, the evaluation of NaCl toleranceof a hybrid of Zea mays ssp. mays (2n=40) and Tripsacum dactyloides (2n=72), was considered of interest to determinethe possibility of using this germplasm in corn tolerance improvement. Long-term organogenic calli, obtainedfrom immature hybrid embryos, have shown high rates of multiplication and plant regeneration. After in vitro treatmentof these calli with different levels of salinity, the survival and regeneration percentages and the daily relativeweight increments were calculated. Regenerated plants were transplanted to pots and watered with NaCl solution (6.1dS m-1) in order to assess tolerance at a whole plant level. Measurements of height, number of leaves per plant, andfresh and dry weights were taken. Exposure to 170 mM NaCl in vitro during 35 days and in vivo during 20 days produceda fresh weight decrease of 51% in calli and 31% in plants, respectively. These results indicate an improved toleranceof the maize/Tripsacum hybrid to salinity stress, in vitro and in vivo, compared with results from previous reportsusing other corn genotypes under similar conditions.

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