Screening for Cold Tolerance during Germination within Sweet and Fiber Sorghums [Sorghum bicolor (L.) Moench] for Energy Biomass

Within the project "BIOSEA" funded by the Italian Ministry of Agriculture and Forestry,a preliminary laboratory test was conducted to assess the variability for cold tolerance duringgermination in 30 cultivars of biomass sorghum, among fiber and sweet types. Seed germination(%) and mean germination time (MGT) were examined at seven constant temperatures (from 8 oCto 35 oC) and base temperature (Tb) and thermal time (?T) for 50% germination were calculated. Awide genetic diversity in the germination response of sorghum was ascertained at 8 oC (CV 45%) and10 oC (CV 25.4%). At 8 oC, in cultivars of 'Padana 4', 'PR811F', 'PSE24213', 'PR849' and 'Zerberus',seed germination exceeded 80%. Seeds of 'Zerberus' were also the fastest, requiring less than 13 daysfor final germination at this low temperature. Great differences were found in Tb and ?T amongcultivars. Tb varied between 7.44 oC ('PR811F') and 13.48 oC ('Nectar'). Thermal time (?T) was, onaverage, 24.09 oCd-1, and ranged between 16.62 ('Nectar') and 33.42 oCd-1('PSE24213'). The bestcombination of the two germination parameters (i.e., low Tb and ?T) corresponded to 'Zerberus','Sucrosorgo 506', 'Jumbo' and 'PR811F'. Accordingly, these cultivars are more tolerant to cold stressduring germination and, thus, more adapt to early spring sowings in Mediterranean areas (MarchApril). Cultivars 'PR811F' (fiber type) and 'Sucrosorgo 506' (sweet type) also combine high coldtolerance with good productivity in terms of final dry biomass, as assessed in open-field conditions(late spring sowing). The genetic variation in the germination response to a low temperature is usefulfor the identification of genotypes of sorghum suitable to early sowings in semi-arid areas. Selectionwithin existing cultivars for cold tolerance during germination may also contribute to the expansionof biomass sorghum into cooler cultivation areas, such as those of Northern Europe, which are lesssuitable to this warm season crop.