Mitigation of Biotic and Abiotic Stresses in Mat Type Seedlings Raised for Mechanical Rice Transplanter

Cold mitigation mechanism at seedling stage is a primary requirement during Boro season as seedlings are raised during months of November and December. This study was conducted at the Sylhet Agricultural University's Agricultural and Biosystem Engineering lab in Sylhet during the 2018-19 academic year. The focus of this study is to mitigate the biotic and abiotic effect on germination and mat-type seedling growing during Boro season. A two-factor design with three replications was used in the experiment. As abiotic stress control factors, six treatments were taken under two different thicknesses (0.04 mm and 0.08 mm) of white polythene sheds that covered day time only (12 hours) and day and night time (24 hours). Along with that two fungicides (Atavo and Autostin) and MoP fertilizer were used to control biotic stress on young seedlings raised in a plastic tray. Agronomical characteristics were measured in two intervals (after 15 and 30 days). The combined effect of 0.08 mm thick polythene shed and MoP treatment showed the highest value for seedling height (167.3 mm), a number of leafs (4), leaf length (99.8 mm), stem length (73.5 mm) and seedling density (18/cm 2 ). Fungal infection was found lowest in 0.08 mm polythene covered day, and night time. Seedling raised plastic trays are much more effective than the conventional way in terms of germination and quality. So, 0.08 mm thick white polythene was recommended as a covering mechanism and MoP as a treating mechanism for seedling rising in cold weather of Sylhet region.

dispersion. Identifying cold stress-induced physiological changes and improving rice breeding for cold tolerance (Zhang et al., 2014). Cold mitigation mechanism at seedling stage is a primary requirement as seedlings are raised during the cold months of November and December during Boro season. To overcome the current seedling raising issue for mechanical transplanting, effective strategies that promote low-temperature stress tolerance (abiotic) during germination and early seedling stages are of great importance to raise mat type seedling of rice during Boro season.
An effective technique for resisting adverse effect of cold weather on rice seedling growth during Boro season is to use polythene shed to protect seedlings from low temperature. Inside temperatures of polythene sheds were recorded at 4 times viz. 6.00 am, 12.00 pm, 6.00 pm and 10.00 pm throughout 21 days of seedling raising period. Plant quality at other treatments was found significantly better than traditional seedling rising without shed (Kamruzzaman et al., 2014). The seed-mats could be prepared in the winter and preserved until the spring seedling-raising period. Seedling mats for the rice transplanted could be created using seed-mats instead of nursery boxes, which take up storage space and require a lot of labor (Hiroyuki et al., 2008). Seeding growing media in the seedling tray has a significant impact on height, leaf number, and thickness of stem. For quality seedlings, soil and manure type, as well as manure mixture ratio to soil and different covering media, are important factors (Shahed et al., 2020).
In order to raise high-quality seedlings that meet agronomical requirements, thereby promoting the use of mechanical translators in Bangladesh. During the irrigated dry season, a study was performed under the proposed research plan with the following objectives: o To develop a mat type seedling rising protocol for Boro season. o To identify suitable grade of polythene to combat low temperature during seedling rising in Boro season. o To evaluate the seedling quality raised under different biotic and abiotic treatments combinations.

MATERIALS AND METHODS:
During the Boro season of 2018-19, this study was carried out at the Sylhet Agricultural University's Agricultural and Biosystem Engineering lab (from 12 December 2018 to 11 January 2019).

Climatic condition of study area
Sylhet's climate is mainly tropical. From April to October, the rainy season is hot and humid, with heavy showers and thunderstorms virtually every day. The rainy season lasts from April to October and is extremely hot and humid, with heavy showers and thunderstorms virtually every day, whereas the brief dry season lasts from November to February and is extremeely warm and clear. Between May and September, about 80% of the annual average rainfall of 4,200 millimeters (170 in) falls (Wikipedia). During the study period December-January temperature was cold and misty.

Ambient temperature and relative humidity
Temperature is an important factor for the growth of rice seedling raised in plastic tray. Ambient temperature during seedling raising period is presented in

General Information Treatments and design
To manage biotic and abiotic stress on mat type rice seedlings, the experiment used a two-factor design with three repetitions. The main factor was the covering mechanism (whole time, night time only and uncovered) of the seedling tray by white polythene of different thickness (0.04 and 0.08mm) available in the markets while treating seeds as well as spray on young seedling immediate after immergence considered as sub-factor of the study. Main and sub-factors were considered to observe the effect of covering and treating mechanism on abiotic and biotic stress, respectively. The treatments arrangement is mentioned as above. Seeds were treated using the fungicide (F 1 and F 2 ) before 10-12 hours of germination. Fungicide was spread on young seedling immediate after seedling emergence (F 3 to F 4 ). Other management was same for all treatments. The agronomic and mechanical parameters of the raised seedling were assessed at 15 and 30 days after sowing. Sprinkler irrigation was used to irrigate regularly throughout the seedling growing period.  Main Factor A to control abiotic stress Factor B to control biotic stress P 1 =Covering by 0.04 mm thickness polythene (day and night time) P 2 =Covering by 0.04 mm thickness polythene (night time only) P 3 =Covering by 0.08 mm thickness polythene (day and night time) P 4 =Covering by 0.08 mm thickness polythene (night time only) and P 5 =Control (uncovered) F 1 =Fungicide-1 (seed treatment) F 2 =Fungicide-2 (seed treatment) F 3 =Fungicide-1 (spraying on seedling) F 4 =Fungicide-2 (spraying on seedling) F 5 =MOP (8-10g/tray) F 6 =control (no fungicide).

RESULTS: Inside temperature of the polythene shed
For protecting the seedling from low temperature, seedling trays were coved by two different thicknesses (0.04 and 0.08 mm) of white polythene sheet. As for abiotic stress control, the seedling trays which are covered by polythene 0.08 mm thickness showed significantly better performance than uncovered trays.
Fungal infection and seedling density were high in covered treys than uncovered treys.

Seedling height Seedling height after 15 days
At 15 days after planting, the interaction effect of abiotic stress factors (mode and method of covering) and biotic stress factors (seed and seedling treatment) had not significant effect on seedling height, although the single effects of abiotic stress factor and biotic stress factor showed opposite ( Table 4). Note: NS-*-significant at 1 %, LoS-Level of significance, Not significant, **-significant at 5 % When seedling trays were coated for 24 hours with both thicknesses of polythene shed and treated with MoP spray. Seedling height was astounding. Both seed and seedling treatments yielded desired results in the case of 0.008 mm polythene shed. On the contrary 24 hours covered and uncovered treys shows poor quality of seedling when covered treys were treated with two different fungicide and MoP ( Table 4).

Seedling height after 30 days
The interaction effect of abiotic (mode and method of covering) and biotic stress control factors (seeds and seedling treatment), as well as the single effects of abiotic stress factor and biotic stress factor, had a substantial impact on seedling height ( Table 5). With 0.08 mm thickness polythene shed covered 24 hours (day and night) and treated with MOP spray, seedling height showed remarkable value after 30 days. Some treatments, on the other hand, did not produce the desired results.

Number of Leaf Number of leaves after 15 days
The two-way interaction of abiotic (covering mode and method) and biotic stress control variables (seeds and seedling treatment) on leaf number was significantly different from the single effect of abiotic stress factor.
While the biotic stress factor has no effect on the number of leaves per plant, ( Table 6). Number of leaves per plant was notable almost all treatment, except uncovered trays. But significantly higher value was observed when 0.04 mm thickness polythene shed was used to cover the seedling tray only day times and 0.08 mm thickness of polythene as well. Seedling treated with fungicide 1 (Atavo) showed better performance than other treatments.  Note: NS-*-significant at 1 %, LoS-Level of significance, Not significant, **-significant at 5 %

Number of leaves after 30 days
Along with the single effect of biotic stress factor, the two-way interaction of abiotic stress control factor (mode and method of covering) and biotic stress control factor (seeds and seedling treatment) had no significant effect on leaf number. Although the single effect of the abiotic stress control factor had a significant effect on the number of leaves, the combined effect of the abiotic stress control factor had a significant effect on the number of ( Table 7). When seedlings were covered 24 hours by 0.04 mm thickness polythene and spray by fungicide 1(Atavo) number of leafs per plant showed significant result. Others covering method also showed desired performance except uncovered trays.

Leaf Length Leaf length after 15 days
Abiotic stress factor (mode and method of covering) and biotic stress factor (seeds and seedling treatment) showed insignificant effect on leaf length combined even though the single effect of abiotic stress and biotic stress factors showed significant effect (Table 8).
Leaf length was higher when seedling was covered 24 hours by 0.08mm thickness polythene with fungicide 2 (Autostin) either sprayed or pretreated before sowing.
The uncovered seedling showed poor performance in all treatment compare to other covering method.

Leaf length after 30 days
Along with the single effect of abiotic stress and biotic stress control factors, a two-way interaction of abiotic stress factor (mode and method of covering) and biotic stress control factor (seeds and seedling treatment) had a significant effect on leaf length (Table 9). When seedlings were covered 24 hours by 0.08 mm thickness polythene and sprayed MoP the leaf length showed significantly higher value than all other treatment. On the other hand, uncovered seedling showed significantly lower leaf length.

Stem Length Stem length after 15 days
Effect of abiotic stress factor (mode and method of covering) and biotic stress control (seeds and seedling treatment) showed significant effect on stem length combined as were the single effect of abiotic and biotic stress control factors (Table 10). Stem length was significantly higher when seedling was covered 24 hours by 0.08 mm thickness polythene shed and treated by MoP spray. Uncovered seedling showed poor performance in stem length. Note: NS-*-significant at 1 %, LoS-Level of significance, Not significant, **-significant at 5 % A=4.57, B=5.01 and A× B=11.21 Note: NS-*-significant at 1 %, LoS-Level of significance, Not significant, **-significant at 5 %

Stem length after 30 days
Interaction effect of abiotic stress factor (mode and method of covering) and biotic stress control (seeds and seedling treatment) did not show significant effect on stem length. Whereas the single effect of abiotic stress and biotic stress factor showed significant effect on stem length (Table 11). When seedlings were covered with 0.08 mm thick polythene shed for 24 hours and treated with MoP spray, stem length increased significantly. In every case, the unprotected seed-ling had a weak stem.

Stem Thickness Stem thickness after 15 days
Along with the single impact of biotic stress control factor, abiotic (mode and method of covering) and biotic stress control factors (seeds and seedling treatment) had no significant impact on stem thickness. Despite the fact that the single effect of the abiotic stress control factor was significant (Table 12). Stem thickness was notable when the seedlings were covered only night time by 0.08mm thickness of polythene and sprayed by fungicide 1 (Atavo).

Stem thickness after 30 days
Effect of abiotic stress control factor (mode and method of covering) and biotic stress factor (seed and seedling treatment) did not show significant effect on stem thickness along with the single effect of biotic stress control. Although the single effect of abiotic stress showed significant effect (Table 13). After 30 days uncovered seedlings showed significant perfor-mance in stem thickness when seed treated with fungicide 1 (Atavo). Note: NS-*-significant at 1 %, LoS-Level of significance, Not significant, **-significant at 5 % Note: NS-*-significant at 1 %, LoS-Level of significance, Not significant, **-significant at 5 %

Seedling density after 30 days
The two-way interaction effect of abiotic and biotic stress control factors, as well as the single effect of biotic stress factor, had no major effect on seedling density. The single effect of abiotic stress, on the other hand, had a significant impact on seedling density (Table 14). Seedling density improved when seedlings were covered for 24 hours with 0.08 mm thick polythene shed and sprayed with MoP. In the case of seedlings in uncovered trays, growth was unsatisfactory.  The lowest length of leaf and stem thickness were found in tray which was kept under 0.04 mm thick blue polythene shed during night and 0.04 mm thick black polythene shed during day and night respectively. However, plant quality at other treatments was found significantly better than traditional seedling rising without shed. Seeding growing media in the seedling tray affects height of seedling, leaf number, stem thickness, and hence plant establishment with few missing hills. For producing high-quality seedlings, soil and manure kinds, as well as the ratio of manure mixture to soil and various covering media, are all considered as critical factors (Shahed et al., 2020). . In case of biotic stress control factors the main aim of this study to use most common and economic fungicide so that farmers can easily manage to take care of their seedling. For treatment two fungicides was used for seed treatment on pre-germinated seeds and also for spraying on newly emerge seedlings. As fertilizer MoP was used. Most of the parameters such as Height of seed-ling, leaf length, stem length, stem thickness, and seed-ling density showed highest result

CONCLUSION:
The mechanical transplanting of rice is gaining popularity day by day. Mat type seed bed preparation is essential for mechanical transplanting of rice seedlings. Either a plastic tray or a polythene sheet can be used to make a mat-style seed bed. Agronomical superior seedlings are an important consideration in the large-scale use of rice transplanted. The current study was conducted using well-prepared dry sandy loom soil and sprouted seeds of BRRI dhan28. The aim of this study to find out appropriate control measure for seedling growth in cold weather of Boro season. Seedling covering mechanism by 0.08 mm thick polythene shed covered day and night time showed best result for all parameters. As sub factor seeds and seedling mechanism showed best result with both fungicide (Atavo and Autostin) when seeds are pretreated before sowing and MoP by spraying in young seedling. So, at last 0.08 mm thick white polythene was recommended for protecting seedling from cold in Boro season. As well as for biotic stress control factor fungicide Atavo, Autostin are recommended in pretreated seeds for preventing fungal infestation.