Llavallol, Buenos Aires, Argentina
Universidad Nacional de La Plata
Lomas de Zamora, Buenos Aires, Argentina
Universidad Nacional de Lomas de Zamora
Exposure of Zea mays, Tripsacum dactyloides and its hybrid Zea x Tripsacum to short periods of chilling (5 C) --Jatimliansky, JR, García, MD, Molina, M del C Maize and Tripsacum are known for their susceptibility to chilling injuries. Maize-Tripsacum F1 plants (2n = 56) have shown more tolerance to chilling temperatures in the field than their parents: Zea mays (2n = 40) and Tripsacum dactyloides (2n = 72). Whilst minimum temperatures of -2 C during 2 days produced irreversible injuries in both parents, no visible damages were observed in the hybrid. A comparative study of the three genotypes was made in controlled conditions to ascertain the different growth behavior of the hybrid relative to its ancestors in the field.

We measured: a) the photochemical efficiency of photosystem (PS) II expressed as the ratio of the variable fluorescence (FV) to the maximum fluorescence yield (FM) (FV/FM ratio) and b) the injuries of the cell membranes of leaves during growth at 5 C or at 25 C by the electric conductivity of solutions due to electrolyte leakage of leaf slices in distilled water.

Maize seedlings were obtained by germination of seeds while Tripsacum and hybrid plants were grown from its rhizomes. When plants were at the four-leaf stage of development, chilling conditions (5 C) were applied in a growth chamber up to 3 days (16 h light - 8 h dark; 400 mol m-2 s-1 PAR at leaf level; 80% RH). Data were analyzed by ANOVA and differences among individual means were compared by the least significant difference (LSD) test.

Table 1. FV/FM ratios in leaves of control (25 C) and chilled (5 C) plants.
 
  maize Tripsacum  maize x Tripsacum
  (2n = 40) (2n = 72) (2n = 56)
Control plants 0.796 a 0.727 a 0.764 a
Chilled plants      
5 C 1 day 0.547 b 0.513 b 0.593 b
5 C 2 days 0.297 cd 0.264 d 0.517 b
5 C 3 days 0.150 e 0.173 e 0.380 c

Means followed by the same small letter are not significantly different (P<0.05) according to the LSD test.

Table 2. Electric conductivity (µS cm-1 g FM-1 hour-1) of leaf slices suspension in distilled water.
 
Genotypes Stressed plants Control plants
  (5 C; 3 d) (25 C)
Zea mays (2n = 40) 71.1 ab 36.7 d
Tripsacum dactyloides (2n = 72) 84.9 a 47.0 cd
Zea x Tripsacum (2n = 56) 61.5 c 35.9 d
Mean 72.5 A 39.9 B

Results of both comparisons indicated that the hybrid was less affected than its parents. After the measures, all chilled plants were cultured at 25 C in the same place as the control plants. After one week, stressed maize seedlings died and, also, leaves from chilled Tripsacum plants, while stressed hybrid plants remained alive as they did in the field.
 
 


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