Influence of Sulfur and Boron on the growth and yield of Broccoli

Broccoli (Brassica oleraceaitalica)is a green edible vegetable in the cabbage family, whose flower head is utilized for cocking. Its cultivation originated in Italy. Broccolo, its Italian name, means "cabbage sprout". Because of its different components, this vegetable provides a complex of tastes and textures, ranging from soft and flowery (the florets) to fibrous and crunchy (the stem and stalk). Its color can vary as deep sage, dark green and purplish-green, depending upon the variety [1, 2]. Broccoli is better adapted to tolerate comparatively high temperature [3]. Unlike cauliflower, broccoli produces smaller flowering shoot from the leaf axile if the main apical flower bud is removed. Consequently afield of broccoli may be harvested over a considerable period of time. This food is very low in saturated fat and cholesterol. It is also a good source of protein, vitamins (A, C, E, K and B6), thiamin, riboflavin, pantothenic acid, calcium, iron, magnesium, phosphorus, selenium, dietary fiber, folate, potassium and manganese. Broccoli also contains large concentrations of caroteniods, which have preventive qualities with regards to human cancer [4,5] demonstrated that fresh broccoli heads contain relatively high levels of glucosinolates and flavonoids that may be chemoprotective against human cancer. Broccoli is a cool-weather crop that does poorly in hot summer weather. It grows best when exposed to an average daily temperature between 18-23 °C [6].It is an important vegetable crop and has high nutritional and good commercial value [7].Nowadays, broccoli attracted more attention due to its diverse use and great nutritional value [8,9]. Broccoli is known as the “Crown jewel of nutrition” for its vitamin rich, high in fiber, and low in calorie properties [10].

Broccoli is grown allover the world. In 2012, total production allover the world was 21,266,789tons. China produced maximum broccoli (9,596,000 tons) followed by India (7,000,000 tons) while Pakistan was at number eight in broccoli production by producing 224,000 tons in 2012[11]. Successful production of broccoli depends on various factors of which fertilizer application is the most important one. Generally, large amount of inorganic fertilizers are applied to vegetable for higher yield and for maximum growth [12,13].

Sulfur, an essential plant nutrient, accounts for 0.2 to 0.25% (20 to 50g kg-1) of plant dry matter. It is rapidly incorporated into organic molecules, the first stable organic S-compound being cysteine, and methionine, are the most important S-containing amino acid in plants which serve as building block of protein[14]. In plants, about 90% amino acids contain sulfur. It is a primary constituent of protein because three amino acids (cysteine, cystine and methionine) contain sulphur. It helps information of chlorophyll. It also helps in synthesis of oil and is therefore very much essential for oilseed crops. It keeps enzymes active and helps in regulation of biochemical reaction. It increases crop yield and improves produce quality [15]. Sulphur is present in soil inorganic and inorganic forms. The organicS accounts for more than 95% of the totalS inmost soils of humid and semi humid regions [16]. The quantity of organic and inorganic Sin a soil sample changes usually according to soil type and depth of sampling. In poorly drained or waterlogged soils, the main forms of inorganic Sin soils is sulfide and often elemental S [17]. Major factors affecting forms of sulphur are organic matter, texture, climate, altitude, salt content, vegetation, leaching, cropping intensity, flooding and carbonates. Transformation of added Sis more complex when organic or elemental/sulfide sources are used as compared to sulfate sources.

Sulphur fertilizers help to enhance the uptake of N, P, K, and Zn in plants. Due to the synergistic effect of Son these elements, their efficiency is enhanced which result in increased crop productivity [16]. Sulphur fertilization is a feasible technique to suppress the plant uptake of undesired toxic elements because of the antagonistic relationship between Sand other elements including Mg, Mo, and Se. Thus S fertilizers are not only useful in increasing crop production and quality of produce but also in improving soil condition for crop growth.

Boron is one of the recognized micro nutrients for plant growth and production. Boron is essential for plant growth and development. It is known to play role in cell division, water relations, ion absorption, IAA and carbohydrates metabolism, translocation of sugars, fruit and seed development and its deficiency may affect all these processes [18,19]. Its application to the soil increased head yield of broccoli [20]. A great deal of attention has been given to studying the effect of B supply on behavior of cations such as K+, Ca++, Mg++ and Na+ in various crop species, but information on the behavior of anions, specially phosphorous, is limited. The early work of [21] indicated that B deficiency in corn and broad beans reduced the capacity for the absorption of POdue to the reduced ATPase activity, which could be rapidly restored by the addition of 4 boron. Later on [22] reported that B plays role in biochemical process in plantse.g. carbohydrates metabolism and transport of sugar through membranes, nucleic acids (DNA and RNA) synthesis, tissue development and formation of cell walls. All these functions are closely related to phosphorous. Therefore, it can be assumed that the borate ions may be fixed in the cell wall as an organic complex and would be responsible for a change in the permeability of the cell wall, resulting in a reduction of phosphate uptake and carbohydrates, under the deficient and toxic conditions of added boron. It deficiency causes many anatomical, physiological and biological changes. Hollow stem disorder is a major problem for broccoli production and is commonly associated with B deficiency [23].

Among the essential micronutrients, boron and molybdenum play vital role in developing the economic plant parts of crop plants. Due to boron deficiency water soaked areas appear on the stem and head surface. Gradually the stem becomes hollow and curd turns brown. Again the molybdenum deficiency appears on young plant with chlorosis of leaf margins and gradually the whole leaf turns white. As a result the leaf blade fails to develop properly and only the midrib portions develop resulting sword like appearance of leaves giving whiptail symptom. Besides, the quantity of boron and molybdenum depend on soil type, soil reaction and the extent of deficiency [24].