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

Abstract

The shedding of young cotton bolls has for many years been widely attributed to nutritional relations; insufficient carbohydrate and nitrogen supplies have most often been thought of in this connection. 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. In 1931, one of the present writers (2) stated that the nutritional dominance of bolls over the vegetative growth of the cotton plant had frequently been observed to inhibit boll setting and terminal bud and branch development. Eaton, in a section of a Field Station report by KING and LOOMIS (17) stated that a very close relation exists between the rate at which organic products are made available by photosynthesis and the number of bolls that the cotton plant retains. 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)

The Role of Endogenous Growth Substances in the Fruiting of Upland Cotton

“…If for any reason this polarity is not established or maintained, shedding results, irrespective of whether or not tissues external to the boll are high, or low, in nutrients (cf. Eaton and Ergle, 1953). Perhaps, as Barlow (1952) suggests, an abscission retarding mechanism is initiated in developing fruit, or alternatively an abscission promoting mechanism is brought into play when development ceases.…”

Mineral Nutrition of the Cotton Plant.

“…The actual nature of the chemical stimuli responsible for the drying up of small floral buds and for the abscission of young bolls remains unknown but it is believed (7,8) that developing cotton bolls secrete a mobile growth-inhibitive substance of anti-auxin nature which causes enough of the bolls to abscise to maintain a balance between fruiting activities and the vegetative stature of the plant. This boll-setting inhibitor is evidently responsible, also, for the suppression of vegetative growth after boll setting has progressed; when the earliest bolls set by well-fruited cotton plants start to open, it is usual for the plant to renew its vegetative growth and at the same time to start to set new bolls.…”

Changes in Amide-Linked and Ester Indole-3-Acetic Acid in Cotton Fruiting Forms during Their Development

“…Stresses, such as water deficit or an inadequate supply of photosynthate, were shown to decrease the free IAA content of young bolls and their abscission zones to even lower values and increase the percentage that abscised (17). Large flower buds and older bolls are much less likely than young bolls to abscise during periods of stress (12,16,22), probably at least in part because they contain much higher concentrations of IAA.…”

“…Cotton (Gossypium hirsutum L.) fruiting forms rarely abscise during the week before anthesis (12,22), but are most susceptible to abscission during the week after anthesis (16,22). Abscission rate then decreases with increasing fruit (boll) age until it is essentially zero at 18 d after anthesis (15,16).…”