Growth and Abscission in Sea Island Cotton

Abstract

With fourteen Figures In the Text. INTRODUCTION.T HE immediate object of the studies reported in the present paper was to obtain information concerning both the external and the internal factors responsible for the premature shedding of the flower-buds and the young fruit (bolls) of the cotton-plant in St. Vincent. The economic importance of premature abscission is not, of course, confined to the cotton-plant, for it is responsible for considerable losses in a large number of cultivated plants. Future investigation may reveal how far the conclusions arrived at in the course of the present work are of wider application.Before reporting the results, reference should be made to the conclusions of previous investigators of the problem. The work of Balls (1) in Egypt established a strong presumption that the major factor initiating abscission was a marked water-deficit in the body of the plant. It was found that the elongation of the stem of the cotton-plant was checked immediately the sun struck upon it, and that a slight shrinkage usually followed. A cloud passing across the sun, for instance, was effective in permitting growth, which ceased again as soon as the sun emerged. Balls's conclusion that a net loss of water was the direct cause of growth-inhibition and boll-shedding received confirmation from Lloyd's (6) studies, which were conducted under the relatively humid conditions of Alabama. Ewing's (2) work in Mississippi also indicated that a disturbance in the water-balaqce of the plant was the main factor responsible for shedding. In St. Vincent, where cotton is probably cultivated under more humid conditions than elsewhere, Harland (3) noted that shedding was heaviest after torrential rain. His observations led him to conclude that root absorption was interfered with as a result of the reduction in the oxygen-

Growth and Development as Influenced by Fruit and Seed Formation

“…These results with the tomato are in complete agreement with those secured with cotton by MASON (17,18), who observed a marked retardation in growth of both the central stem and lateral branches during flowering and fruiting. The rate of elongation of the main axis of the plants decreased in exact proportion to the amount of flowers formed and fruits set.…”

Concentrations of Abscisic Acid and Indoleacetic Acid in Cotton Fruits and Their Abscission Zones in Relation to Fruit Retention

“…The results support the hypothesis that stresses decrease boll retention because they affect the hormonal balance in bolls and their abscission zones. Abscission of cotton (Gossypium hirsutum L.) fruits (bolls) is stongly affected by the balance between production of and demand for photosynthate (10,15,20). The early work of Mason (20) led to the nutritional theory of boll abscission which stated that "the cotton plant retains only as many bolls as it can supply with carbohydrates, nitrogen, or other nutrients" (6).…”

“…Abscission of cotton (Gossypium hirsutum L.) fruits (bolls) is stongly affected by the balance between production of and demand for photosynthate (10,15,20). The early work of Mason (20) led to the nutritional theory of boll abscission which stated that "the cotton plant retains only as many bolls as it can supply with carbohydrates, nitrogen, or other nutrients" (6). Research by Eaton and co-workers (7-9) indicated some inadequacies of the nutritional theory, and much of the subsequent research concentrated on hormonal regulation of abscission.…”

Relationship of Seasonal Trends in Carbohydrate and Nitrogen Levels and Effects of Girdling and Spraying with Sucrose and Urea to the Nutritional Interpretation of Boll Shedding in Cotton

“…This view of the cause of boll shedding is possibly quite old, but the first reference with which the writers are familiar is that of MASON (20) in 1922 in which he said that both the cessation of growth of the main axis and the augimiented susceptibility to shedding could be attributed to a correlation factor which tended to deflect the supply of elaborated food from the apical part of the plant to the fruit developing on the basal fruiting branches. In 1934 MWASON and PHILLIS (21) wrote that the bolls drain the vegetative plant of its food materials, the leaves yellow and fall off as nitrogen is drained away, and as the strain increases the flower-buds and bolls themselves are starved and shed.…”

“…None of the foregoing conclusions was supported by original analytical data but it was known from earlier work that the nitrogen content of vegetative parts of the cotton plant declines with the advance of the summer. 1\ASONN (20) had found that the removal of all leaves caused a prompt shedding of nearly all young bolls carried by Sea Island cotton plants, and EATON (2) had found that when previously set bolls were removed from Upland plants these were replaced within a matter of 10 days with new bolls. HAWKINS et al (15) lfleasured the trends in carbohydrate levels in cotton plants throughout a summer and concluded in 1933 that the percentage of shedding is regulated by the amount of plant food available for the development of the young bolls.…”