Hungary is the northernmost rice-growing country in Europe. Therefore, the monthly mean temperature does not reach 25 °C even during the summer months, which is considered optimal for rice growth. In temperate direct sowing systems, good cold tolerance of varieties is especially importantto reach uniform rice seedling establishment. The cold tolerance testing of the NAIK ÖVKI’s rice variety collection (Szarvas, Hungary) took place in 2018 and 2019 as a result of 10-days cooling periods, respectively. Changes in chlorophyll content of plants were recorded three times during these suboptimal conditions using a Konica Minolta SPAD 502 instrument. The results were grouped according to the different reactions and then plotted in a coordinate system. Based on the obtained results, the indica group was more sensitive to chilling temperature than the japonica group. The most sensitive was the aromatic group, while the cold tolerance of the tropical japonicas did not differ significantly from temperate japonicas at 10.54 °C mean pentad temperature, instead of significant differences observed at 5.8 °C. Eight genotypes were identified (Dunghan Shali, Ábel, Oryzella, Pallagi 77, Risabell/2, Tzjao-Bu-zshi, Jolanda, Chicco), all from the japonica group, which showed no decrease of SPAD values either at 10.54 °C or 5.8 °C. The performance of another 11 varieties (SZV Szellő, Ringola, M225, Fruzsina M, Köröstáj 333, Auguszta, Risabell B/3, Balilla x Sesia/2, Baldo, Opale, CO39) exceeds the standards (M202 and Sandora). CO39 was the only one variety that had good cold tolerance and belongs to indica variety group.

Keywords: rice, cold tolerance, chlorophyll, SPAD