Germination is influenced by many factors, of which temperature, relative humidity and moisture are the key determinants that drives the process of germination. Each crop has its own temperature requirement or optimal temperature that facilitates rapid and uniform germination. However, increase or decrease in temperature form optimal could drastically affect not only final germination per cent but also may increase the time taken to achieve germination
(Rodino et al., 2007). Also time taken from first germination to final germination (uniformity of germination) of a seed lot may increase with fluctuation in optimal temperature which results into non uniform plant growth making inter-cultural operation difficult. For successful and uniform germination of rajmash 20°C is considered optimum (Anonymous, 2015). Therefore, two sub-optimal temperatures
i.e. 10° and 15°C was included in the present investigation to understand the level of cold tolerance in a set of 37 rajmash genotypes. At optimal germination temperature (20°C), there were no significant differences in the final germination and time taken to achieve first germination (T
1) among 37 genotypes, however, these genotypes differed significantly in time taken to achieve 50% germination (T
50), uniformity of germination (U
7525) and mean germination time (MGT) (Table 2). At optimal temperature (20°C), all the genotypes recorded germination percent of >91%, minimum recoded in genotype IC 311670 and maximum (100%) in 12 genotypes (GPR 203, EC 400445, ET 8405, PDR 14, ET 8447, BSLR 2, NO 3160A, BLF 101, UTKARSH, EC 400414, ET 8409 and EC 400401). Time to achieve first germination in 37 genotypes at 20oC varied between 32.11 to 101.38 h with a mean of 67.87 h. Likewise, time taken to achieve 50% germination varied between 67.44 (EC 500232) to 206.26 h (EC 400361) with a mean of 104.58h. Similarly, uniformity of germination (U7525) and MGT at 20°C among 37 genotypes ranged between 2.92-79.93 h and 68.15-208.09, respectively (Table 2 and Table 3).
At first sub-optimal temperature (15°C), genotypes recorded mean germination percent of 96%, minimum (86.10%) recoded in genotype EC 564795 and maximum (100%) in 11 genotypes (ET 8404, ET 8456, BD 9116291, IC 14351, BSLR 2, BLF 101, UTKARSH, EC 14920, EC 400414, EC 150250 and EC 400401). Time to achieve first germination in 37 genotypes at 15°C varied between 50.61 to 133.94 h with a mean of 92.13 h. Likewise, time taken to achieve 50% germination varied between 105.42 (EC 150250) to 172.39 h (IC 25537) with a mean of 137.35h. Similarly, uniformity of germination (U7525) and MGT at 15°C among 37 genotypes ranged between 9.06-63.94 h and 108.06-171.31, respectively (Table 2 and Table 3).
At second sub-optimal temperatures (10oC), two genotypes (ET 8447 and AMBER) recorded 0% germination (100 % reduction from 15 and 20°C) and one genotype (EC 400414) recorded 10% germination (90 % reduction from 15 and 20°C). The germination per cent at 10°C varied between 0-100% with a mean of 77.13%. Genotypes ET 8447 and Amber did not germinate therefore they do not have value for T
1, T
50, U
7525 and MGT. Likewise, there are few genotypes which germinated but did not achieve 50% germination, so they have T
1 value but not T
50. Time to achieve first germination in 35 genotypes at 10°C varied between 99.02 to 425.22 h with a mean of 181.23 h. Likewise, time taken to achieve 50% germination in 31 genotypes varied between 173.18 to 398.18 h with a mean of 272.55 h. Similarly, uniformity of germination (U7525) and MGT at 10°C among 35 genotypes ranged between 12.95-131.55 h and 114.32-382.38, respectively (Table 2 and Table 3).
The proportion of germination at optimal temperature (20°C) had an average value of 98.47% and a minimum value of 91.35 % while first sub-optimal temperature (15°C) had an average value of 96.02% and a minimum value of 86.10% and second sub-optimal temperature (10°C) it had an average value of 77.13% and a minimum value of 0%, which indicates that the genotypes could tolerate cold stress upto 15°C to a considerable level while germination was hampered greatly at 10°C. The emergence was delayed at sub-optimal temperatures by 137.02 and 35.74% at 10 and 15°C, respectively as compared to optimal temperature (Table 2). Genotypes, ET 8447 and Amber were the most susceptible to cold stress as they failed to germinate at 10°C, which otherwise recorded 94.8 and 97.3 % respectively at 15°C and 100 and 96% respectively at 20°C. Likewise, time to achieve 50% germination was delayed by 160.61 and 31.33 times at 10 and 15°C as compared to 20°C, respectively (Fig 1). At 20°C, time taken between 25 and 75% germination to occur (uniformity of germination) was 21.80 h which was increased by 23.39% times at 15°C and by 119.7% times at 10°C (Table 2). Our findings corroborated with Scully and Waines (1987) who reported that rajmash genotypes took about 16-24 days to emerge at sub optimal temperature of 12°C. It has been reported that the activity of alpha amylase gets reduced at low temperature
(Du et al., 2010). The reduction in germination value and increase in the time taken to germinate or attain 50% germination at sub optimal temperature in rajmash may be due to decrease in alpha amylase activity which is essential for breaking down starch and provide food material for germination to occur. At higher temperature the germination rate, speed of germination and seedling emergence will be higher and faster which have been reported in different crops including food legumes, such as soybean, cowpea, groundnut and chickpea
(Craufurd et al., 1996; AwalandIkeda, 2002; Lamichaney and Katiyar, 2017). Slow germination and emergence of rajmash seed at low temperature might attract fungal infection which ultimately leads to seed death before emergence causing poor field emergence and low productivity. Delayed emergence of seeds due to low temperature may lead to damping off diseases which are caused by several soil and seed borne fungi like Pythium, Botrytis, Rhizoctonia, Cylindrocladium, Fusarium, Phoma, Alternaria, Phytophthora
etc (Rodino
et al., 2007).