Top-shoot cuttings were evaluated as planting material with different planting time for rapid multiplication of potato at Bangabandhu Sheikh Mujibur Rahman Agricultural University (BSMRAU) during winter, 2011-2012. The location is situated at about 24˚23' north latitude, 90˚08' east longitude and an altitude of 8.4 m above sea level and adjacent to capital Dhaka city. Potato variety Diamant (BARI Potato-7) was used as test crop. During the growing period maximum and minimum air temperature, relative humidity (%), precipitation and evaporation data were recorded throughout the crop period (Table 1). The air temperature was decreasing in trend from November to January and thereafter increased.

The experiment was laid out in randomized complete block design (RCBD) with three replications. The treatments were: T₁ = Whole tuber planting at 1^st November (1^st Control), T₂ = Whole tuber planting at 1^st November for cutting; T₃ = 1^st cutting from T₂ planted on 25^th November; T₄ = 2^nd cutting from T₂ on 5^th December; T₅ = Whole tuber planting on 10^th November (2^nd control); T₆ = Whole tuber planting on 10^th November for cutting; T₇ = 1^st cutting from T₆ on 5^th December and T₈ = 2^nd cutting from T₆ on 15^th December.

The seed tubers were kept in a well-ventilated room and allowed to sprouting under light at night for obtaining healthy green sprouts prior to planting. In this process, 8 - 10 days were elapsed for sprouting. The sprouted tubers were planted at 1^st November (T₁ and T₂) and 10^th November (T₅ and T₆). T₁ and T₅ were treated as control for producing normal crop. Treatments T₂ and T₆ were used as source of top shoot cuttings. First top-shoot cuttings with at least two nodes were taken from T₂ at 25 days after planting (DAP) which were used as planting material for T₃. Second cuttings were taken from (T₂) at 10 days after first cutting which were used as planting material for T₄. Cuttings were taken by slant cut with a sharp blade and the cut end immerged into water immediately. Then the shoot cuttings were planted in the main plot after treating them with rooting hormone (Napthalene Acetic Acid-16 ppm). Before planting the shoot cuttings in the experimental plots, the plots were irrigated properly so that the cut portion came to the soil and moisture contact. Similarly the top-shoot cuttings were taken from T₆ which were used as planting materials for T₇ and T₈ at 5^th December and 15^th December, respectively.

Full doses of cow dung (10 t∙ha⁻¹), triple super phosphate (220 kg∙ha⁻¹), muriate of potatsh (270 kg∙ha⁻¹), gypsum (120 kg∙ha⁻¹), boric acid (6 kg∙ha⁻¹) and half dose of urea (175 kg∙ha⁻¹) were applied at final land preparation. The rest half of urea (175 kg∙ha⁻¹) was top dressed at 30 DAP followed by earthing up and light irrigation. Ridge method was used for whole tuber planting (T₁, T₂, T₅ and T₆) treatments.

Healthy top shoot cuttings were planted in well watered flat bed. After establishment of the shoot cuttings, ridge was made by earthing up of sides. Intercultural operations such as weeding and earthing up were done manually. Earthing up was done two times, first earthing up was done at 30 DAP when the plant attained a height of about 15 - 20 cm from the base, second time was done at 20 days after the first earthing up. Before the first earthing up, urea was applied. Irrigation was applied five times. The first one was applied at two weeks after planting, the second one was just after earthing up (30 DAP), the third one was at 45 DAP, the 4^th one on 60 DAP, and the last one was at 75 DAP. During land preparation, Furadan 5G was applied 10 kg/ha as basal to control soil borne insects and Malathion (0.2%) sprayed in two installments at 45 and 60 DAP control foliar insects. Dithane-M 45 (0.2%) and Secure (0.1%) sprayed alternately five times at 30, 40, 50, 60, 70 DAP to prevent the late blight disease [13] . Haulm pulling was done at 80 DAP in all treatments. Hardening and setting up of skins of tubers were allowed for 10 days under the soil and there after the crop was harvested at 90 DAP.

Recorded data on tuber yield, grades of tuber by weight and by number were analyzed statistically using the software MSTATC (Developed by the Department of Crop and Soil Sciences, Michigan State University, East Lansing, MI 48824 USA). Significance between treatments were tested by using Duncan Multiple Range Test (DMRT) at p < 0.05 level. Benefit cost ratio (BCR) was calculated according to Khan et al. [14] .

Tuber yield per hectare significantly influenced by planting time (Table 2) and ranged from 18.89 to 42.56 t∙ha⁻¹. Yield decreased in stem cuttings with delayed planting. The highest tuber yield (42.56 t∙ha⁻¹) was obtained from whole tuber planted at 10^th November (T₅) which was statistically similar with planted at 1^st November (T₁) yielded 41.84 t∙ha⁻¹. In case of top-shoot cutting, early planted cuttings (25th November) produced maximum tuber yield of 32.95 t∙ha⁻¹ followed by 5th December planting (25.65 t∙ha⁻¹). The lowest yield (18.89 t∙ha⁻¹) was found in late planted (15th December) cuttings. Tuber yield of potato increased 122.8% (41.84 t∙ha⁻¹ to 93.23 t∙ha⁻¹) from early one source crop due to taking two times cuttings, while it was 89.7% (from 42.56 t∙ha⁻¹ to 80.75 t∙ha⁻¹) from late one source crop. Tuber yield reduced in the treatments T₄, T₃ and T₂ compared to its corresponding control (T₁).

The plants used for cuttings produced from whole tuber planted at 1st November (T₂) showed 17.2 % of yield reduction compared to control (T₁) might be due to two times top shoot cuttings that reduced photosynthetic area and resulted in lower yield. Photosynthesis is positively related with the leaf area and foliage coverage [15] . Many authors previously reported similar results on seed tuber multiplication through top shoot cuttings ( [4] [12] [16] [17] ).

Means bearing same letter in a column do not differ significantly at 1% level of probability.

Again, 21.2% and 38.7% yield reduction was observed in top shoot cuttings treatments T₃ and T₄, respectively. Top-shoot cutting plants needed more time for its establishment and plants got less time to tuber initiation and development resulting lower yield. Similar trend was observed in the treatments T₅, T₆, T₇ and T₈. The yield reduction was higher in the treatments T₇ and T₈ (42.4% and 55.6% respectively) due to late planting of top- shoot cuttings which took more time to establish and simultaneously faced higher temperature which was not suitable for tuber initiation and development [18] . But increased yield was found in T₅ and T₆ (1.7% and 8.3%, respectively) compared to respective T₁ and T₂. It might be due to getting more favorable environment as a result of proper time planting in Bangladesh situation. The crop produced from top-shoot cuttings planted at 5th and 15th December (T₇ and T₈ respectively) showed more yield reduction (26.1% and 26.4% respectively) compared to the cuttings planted on 25th November (T₃) and 5th December (T₄) due to prevailing higher temperature. Early planted tubers favors the better vegetative growth of plants than late planted tubers which ultimately favors the healthier production of top shoots and resulted better establishment of the cuttings [17] . This practice caused production of vigorous plants with better plant height having more number of leaves which ultimately favors in more photosynthesis; a necessary component for obtaining higher yield [19] . Previous studies reported that the yield decreases with delayed planting [9] - [11] . Yield reductions in delayed planting regardless of the precocity and the type of planting materials [20] - [22] . These results are in conformity with the findings of Akhter et al. [23] .

Seed tuber yield increased 167.89% (30.96 t∙ha⁻¹ to 82.94 t∙ha⁻¹) from early one source crop due to taking two times cuttings, while it was 95.33% (from 37.88 t∙ha⁻¹ to73.99 t∙ha⁻¹ cumulative yield) from late one source crop (Table 3). Number of cumulative seed tuber increased from 918519 to 1560741with 69.91% increased from early one source crop due to taking two times cutting, while it was 63.19% (from 923,704 to 1,507,408) from late one source crop.

Planting time of top shoot cutting of potato had significant effects on tuber grade by number (Table 4). Maximum percentage (53.3%) of A grade (28 - 40 mm) seed by number was recorded from T₄ followed by T₇ (53.10%) and T₂ (52.80%) which were statistically similar. The lowest percentage (45.6%) of A-grade seed was recorded from T₃. Highest percentage (36.50%) of B-grade (41 - 55 mm) seed was obtained from T₆ followed by T₅ (33.60%) and T₇ (33.30%). The lowest percentage (24.0) of B-grade seed was recorded in T₂.

Planting time of top shoot cuttings of potato on tuber grade by weight was significant (Table 4). Maximum percentage (70.20%) of A-grade seed (28 - 40 mm) was found in T₈ and minimum percentage (25.50%) of A-grade seed was found in T₃. The highest percentage (65.90%) of B-grade seed (41-55mm) was found in T₆ which was followed by T₄ (63.70), T₇ (61.0%) and T₃ (60.30%). The lowest percentage (21.6) of B-grade seed was found in T₈. The highest percentage (14.20%) of non-seed tuber (<28 mm and >55 mm) was found in T₃ followed by T₅ (11.00%) and the lowest percentage (7.10%) fromT₂.The highest percentage (26.00%) of non-seed (<28 mm + >55 mm) was found from T₁ followed by T₂ (23.20%) and T₃ (22.00%) which were statis-

tically similar and the lowest percentage (13.60%) of non-seed was found in T₇ followed by T₄ (14.7%) and T₆ (16.8%). Potato produced from stem cutting revealed that delayed planting reduced total tuber number and potato grade. These results are in conformity with the findings of [24] [25] .

Variations in benefit cost ratio (BCR) were observed among the treatments (Table 5). In case of top shoot cuttings, high labor involvement required compared to whole tuber planting. In seed production of potato from whole tuber planting, total cost was the highest (Tk. 288,000) in treatments T₁, T₂, T₅ and T₆ and was the lowest (Tk. 119,367) in treatments T₃, T₄, T₇ and T₈. The highest gross return of Tk. 984,440 was found in T₅ and the lowest from T₈ (TK. 443,190).

Considering seed production from top shoot cuttings, total cost was the minimum in the treatments T_3, T₄, T₇ and T₈ and it was Tk. 119,367. The highest gross return of Tk. 739,600 was found in T₃ followed by T₄ (Tk. 597,560). The lowest net return of Tk. 443,190 was found in T₈. The maximum benefit cost ratio (BCR) of 6.20 also recorded from T₃ followed by T₄. The overall BCR was obtained higher in top shoot cuttings than whole

1 USD = 78.30 Tk.

tubers being no required seed cost. Our study revealed that the BCR for whole tuber planting was the highest at mid-November planting and for the top shoots cutting; BCR was highest at early planting of top shoot cutting. Many authors previously reported similar results on seed tuber multiplication [26] - [28] .