Water-logging stress is one of the important abiotic stress in pigeon pea crop especially in low lying areas which damage the crop partially and sometime eliminate the entire crop depending on intensity and duration of water stagnation. The main cause of damage under water logging is oxygen deprivation, which affect nutrient and water uptake, so the plants show wilting even when surrounded by excess of water. In the present study the morphological Scoring (0-3) at the end of water logging stress showed highest score (0) in genotypes IPAC-79 (Check for Tolerant) followed by ICPL-87091, ICP-2376, ICPL-20241, IPAC-212, IPAWL-22-7 and IPAWL-22-8 and may be considered as water logging tolerant. These genotypes showed normal plants after 24,48 and 72 hours of water logging stress imposed (Table 2 and Fig 1) and also showed significantly higher adventitious roots number and adventitious root length over susceptible genotypes and respective normal control (Table 3 and Fig 2). These genotypes also showed development of aerenchyma cells in their roots (Fig 3). Morphologically Leaf senescence, epinasty, plant termination was not observed, the average survival percent was 83.40 and average mortality percent was 16.60 only and affected plants were regenerated (Table 4).
Pigeon pea genotypes like ICP-5028, MA-6 and IPAC-202 showed the score of 01 and were normal up to 24 hours of water logging beyond that they showed only yellowing symptoms even after 72 hours of water logging and further they survived well and these genotypes may be considered as moderately tolerant. The adventitious roots with significant number and length were also found in these genotypes. (Table 2 and 3). Morphologically Leaf senescence, epinasty, plant termination was observed in general, but the average survival percent was 66.70 and average mortality percent was 33.30 only and affected plants were regenerated (Table 3). Pigeon pea genotypes namely MA-3, NDA-1, IPA-15 F, Bahar, IPAC-211, IPA-203, IPAWL-22-6 and IPAWL-22-9 showed lower score (02) and may be considered as moderately susceptible against water logging stress. These genotypes showed normal symptoms on 24 hours of water logging and yellowing after 48 hours and at 72 hours temporary wilting was observed. The adventitious roots with significant number and length were relatively less in these genotypes. (Table 2 and 3). Stressed plants showed Leaf senescence, epinasty, plant termination and average survival percent was 48.60 and average mortality percent was 51.40 and the affected plants were regenerated up to some extent (Table 4). The lowest score (03) was recorded in ICPL-87051, ICP-149, RCM/DD-17, WB-2019/25, WB-2019/26, WB-2019/27, IPAWL-22-1, IPAWL-22-2, IPAWL-22-3, IPAWL-22-4 and IPAWL-22-5 which was at par with ICPL-7035 (Check for susceptibility) and susceptible to water logging stress. These genotypes showed yellowing followed by temporary wilting and finally permanent wilting. The adventitious roots were very less in number and their root length was also very poor. Stressed plants showed Leaf senescence, epinasty, plant termination and average survival per cent was 20.80 and average mortality per cent was 79.20 and the survived plants were regenerated very poorly to some extent (Table 4). Our results are similar with the findings of
Jerald Anthony et al. (2024) in maize imposed to water logging at early seedling stage.
Yield attributes including number of pods/plant, 1000 seed weight (Test Weight) and grain yield/plant were significantly decreased under water logging stress when compared with normal condition (Table 5). Reduction in yield and yield parameters were higher in susceptible and moderately susceptible group of genotypes and lowest reduction in yield and yield components was noted in tolerant (37.02) and moderately tolerant (41.20) group of genotypes (Fig 4). Susceptible and moderately susceptible group showed 59.83% and 42.48% reduction over untreated normal control. Under water logging stress germination and early vegetative stages of pigeon pea are more sensitive to water-logging stress as compared to mature plants. Hence, any plant mechanism that can restore the oxygen supply to the flooded tissues will help in the survival of the plants
(Singh et al., 1986). Crops have to face suffocation throughout their life during water logging due to insufficient of oxygen is a common environmental challenge
(Chaudhary et al., 2011). In flooded soils the gaseous rates of diffusion are 100 times lower than normal
(Sairam et al., 2009) and respiration of plant roots, soil micro-flora and fauna leads to rapid exhaustion of soil oxygen, thereby causing anaerobiosis. According to
Marschner (1995) the genotypes which do not adapt to water logging conditions exhibit symptoms of leaf senescence, whole plant wilting and epinasty followed by a rapid decline or even its termination and in the present investigation these symptoms were noted with mostly susceptible and moderately susceptible genotypes. The reductions in survival rate and increase in mortality rate under water logging has been primarily attributed to anoxia/hypoxia (
Orchard and Jessop 1984). Simulated water logging imposed at early vegetative stages of green gram reduces the yield components and yield
(Saikia et al., 2021) Observations on the development of adventitious roots were recorded in tolerant genotypes after imposing the water-logging treatment and among the tolerant genotypes like ICPL-87091, ICP-2376, ICPL-20241, IPAC-212, IPAWL-22-7 and IPAWL-22-8, the number and length of adventitious roots developed near the root shoot junction were markedly higher over susceptible group. Such adventitious roots were less in number and with small root length or some time absent in Susceptible genotypes like ICPL-87051, ICP-149, RCM/DD-17, WB-2019/25, WB-2019/26, WB-2019/27, IPAWL-22-1, IPAWL-22-2, IPAWL-22-3, IPAWL-22-4 and IPAWL-22-5. These observations showed that tolerant genotypes had adapted to water-logging stress early as compared to other surviving susceptible genotypes. In the present study, the pigeon pea genotypes adapted to water-logging stress developed attributes such as adventitious roots and aerenchyma cells in all tolerant and moderately tolerant genotypes including ICPL-87091, ICP-2376, ICPL-20241, IPAC-212, IPAWL-22-7, IPAWL-22-8, ICP-5028, MA-6 and IPAC-202. These results are similar to those reported by
Pourabdal et al., (2008) in maize,
Thomson et al., (1992) and
Huang et al., (1994) in wheat,
Pires et al., (2002) and
Shimamura et al., (2003, 2010) in soybean. The examination of the transverse sections of the samples showed that IPAC-79, ICPL-87091, ICP-2376, ICPL-20241, IPAC-212, IPAWL-22-7 and IPAWL-22-8 and other surviving genotypes had developed aerenchyma cells, while these cells were absent in the susceptible genotypes ICP7035, ICPL-87051, ICP-149, RCM/DD-17, WB-2019/25, WB-2019/26, WB-2019/27, IPAWL-22-1, IPAWL-22-2, IPAWL-22-3, IPAWL-22-4 and IPAWL-22-5. Water-logging is a widespread production constraint for pigeon pea, especially in high rainfall and poorly drained habitats. The significant biological consequence of water-logging is the deficiency (hypoxia) or complete absence (anoxia) of oxygen in the soil; this sets anerobic conditions and restricts the plant growth and development and consequently the seed yield. The tolerant pigeon pea genotypes can adapt to transient water-logging by inducing certain built-in mechanisms, rapidly assisting plants in their struggle for survival under excess water stress conditions.
Armstrong (1979) demonstrated that the formation of aerenchyma cells, hypertrophied lenticels and adventitious roots facilitate gas diffusion to the roots and thus contribute directly to survival of the plants under water-logging. The common adaptation features of plants to water-logging condition are development of numerous adventitious roots and lenticels with the formation of aerenchymatous cells
(Shimamura et al., 2010). Some insight on the mechanisms of water logging tolerance in pigeon pea, using water-logging tolerant and susceptible pigeon pea genotypes identified earlier by
Sultana et al., (2012). Thus, based on survival data for two years, seven water-logging tolerant (IPAC-79(Check), ICPL87091, ICP2376,ICPL-20241, IPAC-212, IPAWL22-7 and IPAWL22-8), three moderately tolerant (ICP-5028, MA-6 and IPAC-202), eight moderately susceptible (MA-3, NDA-1, IPA-15 F, Bahar, IPAC-211, IPA-203, IPAWL-22-6 and IPAWL-22-9) and twelve sensitive (ICP7035 (Check), ICPL-87051, ICP-149, RCM/DD-17, WB-2019/25, WB-2019/26, WB-2019/27, IPAWL-22-1, IPAWL-22-2, IPAWL-22-3, IPAWL-22-4 and IPAWL-22-5) genotypes were identified. Observations on number of live plants before and after water-logging were recorded to estimate per cent plant survival. In addition, visual scores on plant senescence were also recorded after draining the water. Scoring for senescence was done using a 0 to 3 scale (0.0-Normal 01-Yellowing of leaves, 02-Yellowing followed by T.W. 03-Yellowing followed by T.W. and P.W) following some modification as reported by
Takele and McDavid 1995;
Zaidi et al., 2007). Early pigeon pea varieties are more sensitive as compared to medium and late and the risk of crop failure or yield losses due to short term water logging
(Castanon-Cervantes et al., 1995). Water logging during June September pigeon pea growing season is caused by irregular and prolonged rains and represents an important production constraint and is becomes a serious problem
(Matsunaga et al., 2005). Greater tolerance in the late maturing group is likely to be related to the availability of more time for further recovery from the sub-lethal water-logging stress
(Khare et al., 2002). Besides this,
Hou and Thsenge (1991) in soybean and
Khare et al., (2002) in pigeon pea also correlated flooding tolerance of genotypes with their dark seed coat colour; which was attributed to the presence of greater amounts of tannins in the genotypes. In field peas testa colour and its integrity was also found strongly associated with water logging tolerance (Shahin
et al. 2019) However, in the present investigation no such strong correlation with seed coat colour was observed. The physiological and morphological traits identified in this study would be utilized for further breeding programme in developing tolerant lines as also suggested by
Kennedy et al. (1992) and
Meena et al. (2014a). The findings of
Marschner (1995) and
Orchard and Jessop (1984) suggested that the genotypes which do not adapt to water logging conditions exhibit symptoms of leaf senescence, whole plant wilting and epinasty followed by a rapid decline or even its termination and reductions in survival rate under prolonged water logging has been primarily attributed to anoxia/hypoxia are also observed in the present investigation which supports our findings. The effect of water logging stress on yield related traits in pigeon pea genotypes was also assessed in this experiment. Water logging stress negatively influenced the growth, development and yield by reducing plant height, number of branches, per plant, number of seed per pod, test weight and final economic grain yield. Reduction in these traits is associated with decreased photosynthetic efficiency under stress and plant height and this may be due to decline in cell growth and expansion that limits the overall plant architecture under water logging stress. our findings are also supported with finding of
Kumar et al., 2020, Basavaraj et al., (2023) and
Zhengyuan et.al. (2023). Further the scope of application of Nano technology in enabling plants to overcome water logging stress is yet to be tried (
Mohd kafeel et al., 2023).
