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Sunflower plants at I (vegetative), II (closed flower‐buds) and III (open flower‐buds) growth stages were experimentally inoculated with Sclerotinia sclerotiorum. At the 5th day after inoculation, all plants from I, III and 70 % of II (IIT) did not present wilt symptoms while 30 % of age II plants (IIs) presented severe wilt symptoms in all their leaves and had collapsed. Total soluble phenols were measured in the “lesion” (L) and its “healthy” (H) surrounding zones of all inoculated and control plants. A significant increase in phenols was found in the L and H zones of tolerant plants (I, IIt and III). The corresponding methanolic extracts showed a strong inhibitory effect on the mycelial growth (MG) of the fungus. On the other hand no statistically significant increase took place in the L zones from susceptible plants; their methanolic extracts did not inhibit MG. The chemical analysis of methanolic extracts showed that the isochlorogenic acid was the more inhibitory compound. It significantly accumulated in the L of tolerant plants but did not in those of susceptible ones.

The objective of this study was the evaluation of herbage production and botanical composition of a native grassland, ("flechilla?'), of the Salado River Basin fertilized, during 3 years, with 0, 381, or 762 kg&a-'*yr-' of ammonium sulphate alone or combined with 0 or 208 kg-ha-'*yr-' of triple superphosphate. Annual dry matter accumulation of herbage, (ADMA), was restricted by a negative water-balance in the soil during the first experimental year. A linear response to ammonium sulphate rate, irrespective of triple superphosphate, was observed. In the following years the relationship between ADMA and ammonium sulphate became progressively quadratic, and it was manifest firstly in the plots fertilized with superphosphate. The response to superphosphate seemed to be due to an environmentally stimulated growth demand more than to a phosphorus deficiency in the soil. Ammonium sulphate promoted the growth of gramhtoids and decreased that of legumes and forbs. Superphosphate increased the proportion of legumes and ameliorated the detrimental effect of ammonium sulphate, but only few species reflected the effect of fertilization. Because (a) the sward reacted remarkably to the addition of a nitrogenous fertilizer, and (b) its main legume species, Medicogo polymorpha, (annual), was scarce, it is suggested that the sward's herbage production could be substantially increased by its enrichment with perennial legumes provided that their growth and expansion were assisted by periodic additions of a phosphorous fertilizer. Authors are research scientists, Centro de Ecofisiologia Vegetal (FECIC-CONICET-Fund. M. LILLO), Serrano 661, 1414 Capital Federal, R. Argentina. Authors wish to acknowledge Dr. Ratil Arraras Vergara for having permitted the conduction of the present trial in his farm "El Tr.&ito"and Ings. Agrs. E. Myers, R. Mendoza, a@ Mariana Kade for their invaluable help in the collection of data. Manuscript received April 18, 1980. JOURNAL OF RANGE MANAGEMENT 35(l). January 1982 Thurston, J.M. 1969. The effect of liming and fertilizers on the botanical composition of permanent grassland, and on yield of hay. In: T.H. Rorison (ed.), Ecological Aspects of the Mineral Nutrition of Plants, p, 3-10. Blackwell Scientific Publications, Oxford. Vervoorst, F. 1967. "La Vegetaci6n de la Repiblica Argentina. 7. Las Communidades Vegetales de la Depresi6n de1 Salado. (Pcia. de Buenos Soils". 6th Edition. MacMillan, New York. 567 p. Aires)". Serie Fitogeogritica. INTA. Buenos Aires. 259 p.

SummaryIn Argentina, different areas are suitable for seed potato production: however, each has particular problems, mainly related to different pest and diseases. Tierra del Fuego Island is well isolated from traditional potato growing areas. Therefore, it was tested for its potential for seed production.The cultivars Achatt, Mail6n INTA, Pampeana INTA and Spunta were grown in Rio Grande, San Pablo and Ushuaia from 1991-1994. Nematode presence and aphid population dynamics were recorded. Average tuber yield ranged from 20.1-37.6 t ha -1. After three years PVY and PLRV remained low (0-1% for different cultivars and locations). Moreover. seed tubers obtained were physiologically young. Long days, early frosts and strong winds may limit tuber yield in some years. The island can be considered as an ecological "'safe haven" and is very suitable to obtain healthy and physiologically adequate seed potatoes.

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Plants of the wild species Tagetes rnendocina were regenerated, via organogenesis, from explants and callus cultures, and the occurrence of biocidal metabolites, thiophenes, by such undifferentiated tissues and regenerated plants was investigated. Differences between explant sources were apparent in terms of their competence for dedifferentiation and subsequent organogenesis. Leaf-derived cultures were more responsive than the root-derived ones. Biochemical studies revealed that the plants produced were capable of synthezising thiophene like-compounds following in vitro regeneration.

Koller, D. (Hebrew U., Jerusalem, Israel), H. R. Highkin, and O. H. Caso. Effects of gibberellic acid on stem apices of vernalizable grasses. Amer. Jour. Bot. 47(6) : 518–524. Illus. 1960.—Gibberellic acid was found to have distinct morphogenic effects on the stem apices of 3 vernalizable but unvernalized grasses: Hordeum vulgare var. ‘Kentucky,’ Hordeum bulbosum and Secale cereale var. ‘Winter Petkus.’ In these 3 species, GA caused the activation of lateral meristems on the embryonic nodes of the stem apices, under both short‐ and long‐day conditions. These lateral meristems differentiated into either flower primordia or vegetative shoots. The flower primordia developed almost invariably in Hordeum, while in Secale they seldom did, the apical meristem usually resuming normal vegetative growth after treatment. Despite the occurrence of flowering, it is concluded that the role of GA in this phenomenon is restricted to the activation of lateral meristems in the apex.