ABSTRACT
Studies on spring planting material were started at different sites in highland Balochistan. An initial 104 exotic entries were screened down to nine superior genotypes with higher yield potentials, early maturities, drought, heat tolerance and resistance to yellow rust (Puccinia striiformis). The exotic selected genotypes have better tolerance to drought and heat stresses than the local land race. The results indicated that these improved genotypes could be used for spring planting in highland Balochistan. The selected genotypes have great potential of spring planting particularly for the areas of Quetta, Mastuge, Kalat, Pishin and Muslimbagh due to the greater probability of winter rainfalls and very low probability of the summer/monsoon rainfall.
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DOI: 10.3923/ajps.2002.264.265
URL: https://scialert.net/abstract/?doi=ajps.2002.264.265
INTRODUCTION
In the arid highlands of Balochistan, environmental stresses are the main yield-limiting factors in crop production. Major stresses, which reduce yields are cold and drought in winter and the combined effects of drought and heat and a short growing season during spring. In Balochistan, about 0.79 million ha (53%) of the total cultivated area are used for rainfed agriculture (Nagy et al., 1987). Bread wheat is the main dual purpose cereal crop grown under rainfed agriculture. The likelihood of growing wheat crop successfully under meager rainfall (200-250 mm) is small in the area. However, farmers have strong preference to grow wheat crop for their food security.
Annual total rainfall varies from 150 to 300 mm (Samiullah et al., 2000). Monsoon rains in (Khuzdar and Zhob) between July-August is the main source of moisture for winter planting and under these conditions long duration varieties of wheat are appropriate. However, these ideal conditions occur infrequently in highland areas especially in Quetta, Mastung, Kalat, Pishin and Muslimbagh (Kidd et al., 1988). In most years, because of late winter and early spring rainfall, there is a need to plant wheat crop in early spring. In these situations short duration, drought and heat tolerant genotypes seem to be better alternatives to the long maturity local land races (Rees et al., 1987; Kidd et al., 1988; Ahmad et al., 1990; Samiullah et al., 2000).
At present, the widely used local wheat land race in highland Balochistan is quite well adapted to winter planting, being of longer duration, but it is susceptible to yellow rust (Puccinia striiformis), terminal cold and is low yielding (Samiullah et al., 2000). Farmers have the only option to use the same material for spring planting. Local wheat land race Kahani was an option for spring planting but this landrace is almost diminished in the area due to the prolonged drought conditions in the region. Spring planted crops are usually less productive in this area because winter planted crops have comparatively better water use efficiency. This is because winter planted wheats are able to escape, to some extent, heat and drought stresses during their reproductive stages, whereas, spring sown crops usually suffer more from terminal drought and high temperatures. These environmental stresses on plants can be reduced by selecting genotypes better adapted to the harsh prevailing biotic and abiotic stresses of highland Balochistan coupled with better agronomic practices.
Selection of adapted short maturity genotypes of wheat more resistant to drought, heat and diseases is one of the on-going research activities of the Arid Zone Research Center (AZRC) in collaboration with the International Center for Agricultural Research in the Dry Areas (ICARDA). This paper reports progress made in the initial screening and selection of desirable wheat suitable for spring planting and their agronomic performance on farmer's fields.
MATERIALS AND METHODS
Four principal locations (Quetta, Kalat, Kan-Metharzai and Khuzdar) were used for multi-year testing of exotic genotypes from 1986-89 under a range of climatic conditions experienced in the spring cropping areas of highland Balochistan. Initially, one hundred and four entries were planted at Khuzdar in early spring for screening and selection of desirable genotypes. This nursery was planted in single rows of 5 m length with a row spacing of 0.25 m. On the basis of observation on drought, heat tolerance and yield potentials, 19 genotypes were selected for further studies. The selected genotypes were advanced to yield trials and were exposed to a wide range of multi-location environmental stresses.
Each year planting was done in late winter to early spring (late January to early February) depending on rainfall occurrence using a single row hand drill. Yield trials were laid out as Randomized Complete Block Designs (RCBD) with a plot size of 1.5 x 5 m2 and 0.25 m row spacing. If rains do not occur or became to late at the time of planting, crops were sown after pre-soaking irrigation to allow uniform plant establishment. If the drought prolonged an irrigation (100 mm approximately) was applied at grain formation to ensure seed production for next season planting. The total rainfall during the experiment does not exceed 200 mm. Fertilizer was applied at the rate of 60 kg ha-1 N and 60 kg ha-1 P2O5 at the time of sowing.
The crop was harvested by hand between June and July, depending on site elevation. The four middle rows were harvested in each plot to measure total dry matter production (TDM) and grain yields. For yellow rust disease Modified Cobb Scale was used. All the data were analyzed on computer using MSTAT-C package.
Three genotypes (WAT86 1003, WAT86 1007, WPT86 1216) were also tested on farmers field at Dasht and Mastung AZRC research farm from 1996-98. The trials were planted with the tractor mounted AZRC modified Oyjord plot planter in a RCBD. Plot size was 2 x 12 m2 having 5 rows per plot (40 cm row spacing) and ridge furrow system. Seed rate was 100 kg ha-1. This operation was carried out to accord with the local farmers practices of moisture conservation and proper seed placement. Data on fresh biomass at flowering, total dry matter production (TDM), straw production and harvest index were recorded.
RESULTS AND DISCUSSION
Grain yield differences among the genotypes were significant (P<0.05) when averaged across the years, while TDM production did not differ significantly. The exotic genotypes (WAT86 603, WAT86 613, WAT86 620, WAT86 923, WAT86 1003, WAT86 1007, WPT86 1216 and WAT86 93) significantly out-yielded the local check. Their mean grain yields ranged between 515 to 769 kg ha-1 compared to the yield of local check, 395 kg ha-1 (Table 1). The total dry matter production of these entries was also better than the local check. These exotic genotypes were better adapted to the harsh environment of highland Balochistan when planted in spring. All the exotic genotypes have shown better resistance to leaf and yellow rust than the local check (Table 2). Biomass production, total dry matter, grain yield, straw production and harvest index of three tested genotypes (WAT86 1003, WAT86 1007, WPT86 1216) were not significantly (P>0.05) different than the local check. However, all the three genotypes showed better performance for biomass production, total dry matter, grain yield and straw production than the local check (Table 3). Genotypes WAT 1216 produced highest grain yield of 857 kg ha-1 compared to 520 kg ha-1 of local check (Table 3).
Results from the multi-location testing of exotic genotypes in highland Balochistan indicated that the yield potential of spring sown crops was limited mainly by drought, heat and the shortness of the growing season.
Table 1: | Mean total dry matter (TDM) and grain yield (kg ha-1) of 20 bread wheat lines tested at different sites in highland Balochistan (Averaged over 7 different environments). |
1Means within the same column followed by different letters are statistically different at the P=0.05 level of significance. |
Table 2: | Rust reaction of top nine bread wheat genotypes in adult stage at Quetta, NARC and Pirsabak |
MRMS = Moderate resistant to moderate susceptible, MSS = Moderate susceptible to susceptible, MS = Moderate susceptible, S = Susceptible RMR = Resistant to moderate resistant |
Table 3: | Biomass production, total dry matter (TDM), grain yield, straw production (kg ha-1) and harvest index (%) of exotic genotypes at Dasht and Mastuge (averaged over 2 environments) |
However, resistance to cold in the early stages of growth is also essential because temperatures below freezing are usually experienced at the tillering stage of the crop; frost or cold damage at this juncture reduces the tillering capacity of the crop, which in turn reduces the final seed production of spring planted crops (Nachit, 1984). However, low tillering genotypes are better suited to the short growth cycle in moisture stressed environments. Therefore, genotypes with high kernel weight and/or higher kernel number per spike, would be a more desirable type for spring planting. Some years an unusual frost also occurred during grain filling stage in Balochistan which resulted low grain yield due to reduced seed setting or spike sterility (Single, 1985). At this growth stage, the chances of recovery is very rare because crop also enters periods of high temperature and water deficit. However, the occurrence of such late frost at reproductive stage in highland Balochistan is rare. The selected genotypes have an erect growth habit. Such genotypes usually do not require vernalization and grow faster than types with prostrate growth habits (Ahmad et al., 1990). Moreover, the selected genotypes have early growth vigor and early maturity than the local check. Such genotypes have better water use efficiency due to their faster early growth rate and early maturity enabled them to escape terminal drought stress (Fisher and Maurer, 1987). These characteristics displayed by the selected genotypes made them a good option for the farmers of the area having low summer/monsoon rains probabilities.
The local wheat landrace is highly susceptible to yellow rust. Therefore, screening and selection of improved genotypes for disease resistance particularly yellow rust, must be another important objective in Balochistan. During the trials, yellow rust appeared in epidemic form, which provided good natural conditions for screening the material. At NARC and Pirsabak, the selected genotypes showed moderate resistance to yellow rust. However, selection was made particularly for highland Balochistan. Therefore, consideration was given for selecting the disease resistant genotypes against the prevailing yellow rust race of Balochistan.
Exotic genotypes produced higher biomass than the local check. Higher biomass production is dryland agriculture is a desirable trait because such genotypes have better water use efficiency due to their greater proportion of crop growth early in the season. Moreover, grain yield is also related to biomass production in late vegetative/early reproductive stage except in very severe post-anthesis drought conditions (Fischer, 1979). In water limited areas, genotypes possess characteristics of drought tolerance/resistance are of much importance than maximizing yield in favorable environments (Srivastava, 1987). In Balochistan, biomass and straw production is equally important as grain yield. In very dry seasons, if crops do not produced grains than straw has a considerable value for livestock. In Balochistan, raising of small ruminants coupled with dryland agriculture is the main income earning source of the farmers and in such a crop-livestock production system straw products also play a major role in the economy of the area.
The results indicated that if the rains arrives late in the season, but is abundant, farmers could advantageously use early maturing genotypes to reduce the risk of crop failure coupled with better moisture conservation practices. With the increasing population growth rate, it is essential to bring the arable land of Balochistan under cultivation by understanding the major production constraints of dryland and by developing ways to alleviate them. This research highlights a positive step towards selection of short duration varieties with high yields and disease resistance for highland Balochistan. The research trials conducted on farmers field serves the purpose of demonstration and act as focus for discussion of agricultural problems. This makes the technology directly available to farmer's conditions without any further delay. Further studies are required to determine appropriate seed rate, response of planting dates and fertilizers with supplemental irrigation.