Research activities conducted on tobacco during the year 2005/2006 are presented under the themes; Introduction and evaluation of improved germplasm, Productivity and quality improvement and disease management.
Introduction and evaluation of improved germplasm
1. Demonstration of promising flue–cured tobacco varieties
The promising characteristics of the two flue-cured tobacco varieties Speight G70 and Coker 371 Gold were demonstrated in two trials conducted at Rivière du Rempart and Richelieu Crop Research Station (CRS) in the first and second seasons of 2005 respectively. The main objective was to facilitate limited release of the varieties to progressive planters. Each trial was laid down in a randomized complete block design with 3 replicates over an area of 486m2. Variety RG13 was used as the control.
Results (represented in Table 1) showed that at Rivière du Rempart, green and cured leaf yields were significantly higher in Coker 371 Gold than in Speight G 70 and RG13. Averaged over both sites, Coker 371 Gold scored the highest grade index (101.9 Rs/kg) compared to Speight G70 (96.6) and RG13 (99.5). Days to 50% flowering was significantly earlier by 3 days and 9 days in Speight G70 than RG13 and Coker 371 Gold respectively.
Among the 3 varieties, Coker 371 Gold was the most outstanding and could thus be recommended for commercial release. Speight G70 being early maturing can also be recommended for commercial growing especially in the second season given that the duration for land rent is shorter. Henceforth, in addition to RG13, tobacco growers can rely on both Coker 371 Gold and Speight G70 to boost up their productivity.
2. Agronomic evaluation and screening of 3 light air-cured tobacco varieties
The objective of this trial is to compare the yield and quality performance of the light air-cured varieties CSC 300, CSC 301 and CSC 302 with the commercial variety Amarello under farmers' conditions. Seedlings were field transplanted at Bramstan on 25.05.05 in a randomized complete block design with 3 replicates over a total area of 270m2.
Visual assessment of the crop six weeks after transplanting showed leaf curling, leaf mottling and apical bud deformation. Following ELISA tests, all varieties were PVY positive with percentage incidence above 90%. Yield parameters could not be taken given that growth was stunted and leaves were small and uncurable. The trial was repeated at Richelieu CRS from September 2005 to February 2006.
The 3 light air- cured varieties produced significantly higher green leaf yield and leaf number/plant than Amarello implying that their growth and yield characteristics are at par. Days to 50% flowering was significantly longer in CSC 302 and might thus account for its highest leaf number (Table 2).
Multi- locational yield trials will be conducted during the 2006/2007 cropping seasons to screen for the most promising variety.
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Table1: Performance of promising flue cured tobacco varieties Coker 371 Gold and Speight G70 at Rivière du Rempart and Richelieu in 2005/2006
Rivière du Rempart / RichelieuVariety / Grade Index (Rs/kg) / Cured leaf yield (kg/ha) / Green leaf yield (kg/ha) / Plant height (cm) / Leaf number/ plant / Days to 50% flowering / Grade Index (Rs/kg) / Cured leaf yield (kg/ha) / Green leaf yield (kg/ha) / Plant height (cm) / Leaf number/ plant / Days to 50% flowering
Coker 371
Gold / 94.0 / 2368a / 12,863a / 83.5 / 20.3a / 59.0a / 109.9 / 2680 / 19,151 / 95.4 / 21.0 / 62.7a
Speight G70 / 88.0 / 1797b / 11,796b / 79.7 / 18.7b / 53.0c / 105.3 / 2661 / 17,626 / 84.5 / 20.2 / 57.3b
RG13 / 92.0 / 1810b / 12,250b / 77.2 / 17.3c / 56.0b / 107.0 / 2790 / 19,928 / 88.9 / 18.8 / 59.7c
SE± / 1.65 / 63.64 / 215.81 / 2.83 / 0.27 / 0.47 / 2.68 / 108.1 / 698.5 / 3.52 / 0.90 / 072
P
(<0.05) / n.s / s / s / n.s / s / s / n.s / n.s / n.s / n.s / n.s / s
Means followed by the same letter are not significantly different by the LSD test.
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Table 2: Growth and yield characteristics of air-cured varieties under test at Richelieu CRS in 2005/2006.
Variety / Cured leaf yield (kg/ha) / Green leaf yield (kg/ha) / Leaf Number/plant / Plant Height (cm) / Days to 50% floweringCSC300 / 1643 / 16270a / 37.3ab / 147.8 / 72.3b
CSC301 / 1708 / 15958ab / 35.2b / 143.7 / 71.7b
CSC302 / 1570 / 15842ab / 39.3a / 144.8 / 79.3a
Amarello / 1525 / 13385b / 29.4c / 129.4 / 65.7c
SE± / 52.88 / 381.78 / 0.97 / 5.99 / 1.21
(P<0.05) / n.s / s / s / n.s / s
Means followed by the same letter are not significantly different by the LSD test.
3. Productivity and quality improvement
Investigation on leaf disorder in flue-cured tobacco
(i) Investigation on phytotoxicity in soils of La Lucie and Clavet
For the last two successive years (2003 and 2004), growers of flue-cured tobacco who planted on land available by the Deep River Beau Champ Sugar Estate for the second season have suffered serious economic losses from the leaf disorder. To avoid the problem recurring for the crop 2005/2006, lands from new regions namely La Lucie and Clavet will be released for tobacco cultivation. At the request of the Tobacco Board, AREU conducted a field study to determine the likely phytotoxicity in soils of La Lucie and Clavet that would result in the characteristic interveinal yellowing and necrosis on tobacco seedlings.
In June 2005, 72 composite soil samples at depth of 20cm were collected in 24 fields in La Lucie (25ha) and Clavet (20ha) 35 – 40 days before sugar cane harvest. The soils were used in a pot experiment at Richelieu CRS to observe the incidence of tobacco leaf disorder, if any, on seedlings of the variety K326.
Observations which started as from June 2005, revealed the incidence of the leaf disorder as characterized by symptoms of interveinal yellowing and necrosis which were apparent at 38 days after transplantation (DAT) in soils of La Lucie only. After 56 DAT, the incidence reached 42% at La Lucie and 3% at Clavet. From there onwards, the incidence did not progressed further.
Conclusion
This study showed the presence of phytotoxicity in the soils of La Lucie and Clavet and the incidence of leaf disorder was higher at La Lucie than of Clavet.
Recommendation
In the light of the above, tobacco plantation for the second season 2005/2006 should be avoided at La Lucie and Clavet.
A simulation of sugar cane applied herbicides in flue-cured tobacco.
Following the likely phytotoxicity of residual herbicides in soils of Deep River Beau Champ Sugar Estate (DRBC SE) (vide Report on Investigation on leaf disorder in flue-cured tobacco, July 2005), a trial was set up at Richelieu CRS from October 2005 to March 2006 to investigate further whether herbicides currently used by DRBC SE for weed control in sugar cane are responsible for leaf necrosis on flue-cured tobacco seedlings.
A pot of land of 600 m2 kept fallow for one year was selected and the herbicides Tebuthiuron (Tebusan), Diuron (Karmex flo) and Trichlopyr (Garlon) were applied in tobacco furrows on 11th October 2005 at ½, ¼ and 1/8 recommended rate. Tobacco seedlings of the varieties K326, RG 13 and SPG 28 were transplanted at 2 time intervals: 1 week and 1 month after herbicide application (AHA). The delayed transplantation were meant to confirm for residual effect of the herbicides and the inclusion of the three varieties to assess their degree of susceptibility to the herbicides. The crop was monitored twice weekly as from transplantation. Results are discussed below:
1st planting interval:
For the 1st planting interval (1week AHA), complete kill of seedlings was observed 3-5 days after transplantation with Garlon only at ½ and ¼ recommended rates. Interveinal yellowing was apparent on the leaves 42- 45 days AHA with Tebusan and Diuron at all 3 rates and with Garlon at 1/8 recommended rate. The incidence of the leaf disorder was highest with Diuron at ½ and 1/8 recommended rates (Table 3).
Table 3: Percentage of plants showing the leaf disorder symptoms at the 1st planting interval (1 week AHA) with different herbicide treatments at 3 application rates.
% incidence of leaf disorderRG 13 / K326 / SPG 28
½ / ¼ / 1/8 / Mean / ½ / ¼ / 1/8 / Mean / ½ / ¼ / 1/8 / Mean
Tebusan / 11.0 / 18.0 / 27.0 / 18.6 / 15.0 / 20.0 / 26.0 / 20.3 / 14.0 / 16.0 / 30.0 / 20.0
Garlon / nil* / nil / 42.0 / 14.0 / nil / nil / 45.0 / 15.0 / nil / nil / 40.0 / 13.3
Diuron / 72.0 / 39.0 / 80.0 / 63.7 / 65.0 / 41.0 / 82.0 / 62.7 / 68.0 / 36.0 / 82.0 / 62.0
* 100% mortality 3-5 days after transplantation
2nd planting interval
Similarly, at the 2nd planting interval (1 month AHA), 100% mortality was observed with Garlon only at ½ and ¼ recommended rates. The characteristic interveinal yellowing were observed on lowermost leaves 67- 70 days AHA with Tebusan and Diuron at all 3 rates and with Garlon at 1/8 recommended rate. The incidence of the leaf disorder was highest with Diuron at ½ and ¼ recommended rates (Table 4). At both planting intervals, all 3 varieties were susceptible to the herbicides.
Table 4: Percentage of plants showing the leaf disorder symptoms at the 2st planting interval (1 month AHA) with different herbicide treatments at 3 application rates.
% incidence of leaf disorderRG 13 / K326 / SPG 28
½ / ¼ / 1/8 / Mean / ½ / ¼ / 1/8 / Mean / ½ / ¼ / 1/8 / Mean
Tebusan / 7.5 / 4.0 / 4.5 / 5.3 / 6.5 / 4.0 / 6.0 / 5.5 / 7.4 / 4.7 / 6.8 / 6.3
Garlon / nil* / nil / 12.7 / 4.2 / nil / nil / 11.0 / 3.7 / nil / nil / 11.5 / 3.8
Diuron / 82.0 / 78.0 / 44.3 / 68.1 / 79.0 / 74.0 / 48.0 / 67.0 / 80.0 / 72.0 / 46.4 / 66.1
* 100% mortality 3-5 days after transplantation
Conclusion
-The results indicated the presence of herbicide residues in the soil and hence the likeliness to trigger the symptoms of interveinal yellowing on the tobacco leaves.
-Herbicides Diuron and Tebusan which are photosynthetic inhibitors and are taken up into the plant via the roots might be responsible for the leaf disorder symptoms.
Seedling production in tobacco
Comparative performance of flue-cured tobacco seedlings raised under the traditional system and the innovated technology.
The early establishment and yield of flue-cured tobacco seedlings raised under the traditional system (seedbed) and the innovated technology (seed trays) were compared at Richelieu CRS in the first season of 2005. Naked tobacco seeds of variety K326 were sown in 200-module seed trays with the E-Z seedsower using 2 different media: (i) scum and (ii) soil + farmyard manure (3:1 w/w). Seeds sown on seedbed were used as the control. Sowing was effected on 31st April 2005. Seedlings were field transplanted in May 2005 and the experiment was laid down in a randomized complete block design with 3 replicates over an area of 260m2. At seedling stage, seedlings vigour was assessed and at harvest, growth and yield were observed. These are discussed below:
1. Seedling vigour
Percentage (%) germination was significantly higher in scum (79.7%) as compared to soil + FYM (43.4%) whereby seedlings emerged three days later. This might be due to the compaction of the medium which retarded seedling emergence. Aboveground biomass (leaf length, shoot height and shoot weight) was significantly higher in seedlings raised on seedbed while root weight was relatively higher in seedlings raised in seedtrays. (Table 5)
Table 5: Early establishment of flue-cured tobacco seedlings raised on seedbed and in seed trays (under scum, soil + FYM) at Richelieu CRS in 2005.
Scum / 79.67a / 10.00 / 3.43 / 2.93 c / 0.50 b / 0.35 b / 0.18
Soil + FYM / 43.33 b / 13.00 / 3.67 / 2.29 b / 0.50 b / 0.24 b / 0.11
Seedbed / 71.67 a / 10.00 / 3.97 / 4.61 a / 1.01 a / 0.87 a / 0.03
SE ± / 3.84 / 0.22 / 0.23 / 0.01 / 0.05 / 0.04
P (<0.05) / s / ns / s / s / s / ns
2.Growth and yield characteristics
Although days to transplanting was earlier by 1 week with seedlings raised on seedtrays, they reached 50% flowering at the same time interval as seedlings raised on seedbeds. This might be ascribed to the lower above ground biomass of the seedlings at the time of transplanting. Differences in growth and yield characteristics (plant height, leaf number at topping, green and cured leaf yields) were not significant between the treatments (Table 5).
Table 5: Growth and yield characteristics of flue-cured tobacco raised on seedbed and in seed trays (under scum, soil + FYM) at Richelieu CRS in 2005.
Treatment / Days to transplanting / Days to 50% flowering / Plant height (cm) / Leaf number at topping / Green leaf yield (kg/ha) / Cured leaf yield (kg/ha)Scum / 46.0 / 70.0a / 88.5 / 18.3 / 8986 / 1164.3
Soil + FYM / 46.0 / 70.7a / 86.7 / 17.0 / 8275 / 957.3
Seedbed / 53.0 / 62.0b / 87.7 / 16.3 / 8159 / 920.0
SE ± / 0.79 / 1.77 / 1.52 / 838.56 / 90.20
P (<0.05) / s / ns / ns / ns / ns
Conclusion
1. Scum was found to be a better sowing medium than soil + FYM.
2. Days to transplantation was earlier by 1 week in seed trays than in seedbed.
However, no comparative yield difference could be made between seedlings raised on seedbeds and in seed trays.
In future trials, tobacco seeds sown in seed trays will be raised under greenhouse conditions to better assess their performance with the conventional system.
Disease Management