Botany

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Browsing Botany by Subject "Cultivars"

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    A comparative study of certain cultivars of manihot esculenta crantz with special reference to certain morphological characteristics, photosynthesis and water relations.
    (1992) Zobolo, Alpheus Mpilo; Boshoff, D.N.
    Cassava {Manihot esculenta Crantz) is cultivated for its tuberous roots. In this study four cultivars MSAF 2, CMC 40, M 170 and M 5 were compared for their yield and morphological and physiological characteristics. The cultivars were planted in the field and in pots. Photosynthesis and transpiration were measured using a portable Infra - red C02 analyser. The leaf chamber had an area of 1120 mm2. Measurements were made between 9:30 and 15:30. The leaf area was determined using a AT area meter. The leaf water potential was measured with a pressure bomb. The chlorophyll a was extracted with 90 % acetone and determined spectrophotometrically. The drying of the plant material was done at 105 °C in an oven. The photosynthetic rate decreased from top to bottom within the plant's canopy. The maximum photosynthetic rate obtained ranged from 8,4 to 10,97 umol CO* m~a s"1. CMC 40 had the lowest leaf photosynthetic rate. The winter retention of LAI and photosynthesis were the lowest in CMC 40. The photosynthetic rate was high in the morning and declined in the afternoon. In MSAF 2 the photosynthetic rate decreased when the leaf water potential was below -0,5 MPa. in CMC 40, M 170 and M 5 the photosynthetic rate decreased when the leaf water potential was below -0,6 MPa. A decrease in the photosynthetic rate with a decreasing leaf water potential was followed by a decrease in the relative transpiration rate in MSAF 2. CMC 40 had the lowest transpiration rate. The chlorophyll a content was lowest in CMC 40- The maximum chlorophyll a content ranged from 0,96 to 1,19 |ig mm-2 in field plants and from 0,32 to 0,40 \iq mm_a in potted plants. The chlorophyll a content was high during the first growth season and declined in post winter regrowth in all the cultivars. Plant height, leaf numbers, LAI and the partitioning of dry matter followed a seasonal pattern in all the cultivars. The total dry mass increased as LAI increased up to 1/31 in potted plants and up to LAI 2,42 - 6,14 in field plants. In the first year of growth in field plants, the tuber dry mass increased with LAI up to levels of 2,29 - 3,61, then declined. In the potted plants, the tuber dry mass increased with LAI up to 1,2 and continued to increase in spite of the decline in LAI, which was still close to 0,8. At 707 DAP, MSAF 2 had the highest root dry mass while CMC 40 had the lowest. The maximum tuber dry mass obtained was 110-353 g m"a in potted plants and 2505-3577 g m~a in field plants. The number of tubers per plant was highest in M 170 (7,5¬ 9,4) and lowest in CMC 40 (3,2 - 4,25). MSAF 2 was intermediate (6,25 - 6,6). CMC 40 and M 5 had a higher stem dry mass than M 170 and MSAF 2. Except for a few exceptions, a significantly higher LAI resulted in a significantly higher root yield only if it coincided with a significantly higher HI. The maximum HI ranged from 0,7 - 0,8 in field plants and from 0,39 - 0,82 in potted plants.
University of Zululand