Abstract
In vitro screening of 30 potato genotypes for heat stress was conducted. In vitro potato plants were evaluated on the basis of their growth, microtuberization and biochemical analysis under different temperature treatments (12 degrees C, 24 degrees C and 30 degrees C). Both in vitro high (30 degrees C) or less than normal (12 degrees C) temperature degrees significantly affected plantlet length, number of nodes/plantlet and root number. Plantlet height at high temperature (heat stress) was significantly reduced (ave. 2.9 cm) while, less than normal temperature did not decrease plant height and was comparable to the control treatment (24 degrees C) (ave. 5.7 vs. 5.5 cm). In addition, microplants grown under 30 degrees C had significantly less both number of nodes and root number per plantlet in contrast to control condition, supporting the idea of the unfavorable effect of heat stress on potato growth. As an average over all tested genotypes, the number of microtuber/jar was significantly affected by temperature treatment. The lowest recorded number (ave. 1.44 microtubers) was observed when in vitro potato plants were grown under high temperature as a heat stress treatment. Potato genotypes were found to be significantly different in their microtuberization potential. Our results indicated profound significant interaction between in vitro temperature degrees and genotypes concerning microtuber formation and development. All genotypes produced microtubers at 24 degrees C and at 12 degrees C, while some genotypes were not able to form microtubers due to the heat stress exposure. On the other hand, the cvs. Fridor, Lady Rosetta, Agria and Picasso had higher microtuber number/jar at 30 degrees C compared to the control or low temperature and may be considered as tolerant to high temperature stress. Under high temperature stress, all photosynthetic pigments were significantly lower than the control. At this high temperature, chl. a, b, total chl. and carotenoids represented 82.4%, 69.3%, 76.3% and 70.5% of the control, respectively. These results indicated that heat stress adversely affecting photosynthetic pigment contents compared with growth under normal or less than normal temperature degrees. Heat stresses significantly decreased total amino acids and proline contents; however it activates SOD and CAT enzymes. In current investigation, results showed heat stress significantly reduced tuberization in the majority of genotypes. However, few genotypes showed superior growth and microtuberization under heat stress condition and may be used as stock genetic material in breeding programs for producing elite potato genotypes adapted to heat stress.