2.1. Plant materials and growth conditions
The four spring wheat cultivars (T. aestivum L.) used in this
study were Postelberger Wechsel St. 7 (PWS7), Kloka KM 1353
(KKM1353), C518 and Kamysinskaja 3 (KK3) received from the
Institute of Plant Genetics and Crop Research (IPK, Gatersleben,
Germany). The origin of the first two cultivars is Germany and the
latter two are from Pakistan and Soviet Union, respectively. The cultivars
were selected on the basis of the effect on Fv/Fm after 2 h of
38 ◦C heat stress on young plants, in a large-scale screening experiment
on 1274 cultivars (Sharma et al., 2012), where the cultivars
C518 and KK3 were tolerant and PWS7 and KKM1353 were less
tolerant as expressed by lower Fv/Fm after the heat stress.