Lupins, a New Host of Phytophthora erythroseptica.

Several lupin (Lupinus) species are native to southern Spain (2). The white lupin, Lupinus albus L., is the most important crop, and its seeds are used for human consumption and animal feed. Accessions of three indigenous species, L. albus, L. angustifolius L., and L. luteus L., and an introduced species from South America, L. mutabilis Sweet, were planted during October in replicated yield trials in acidic soils (pH 6.5) in the Sierra Morena Mountains (elevation 350 m) north of Córdoba. Root and crown rot disease was widespread and very serious on the indigenous lupins, particularly in several patches of white lupin cultivars. Infected plants were devoid of feeder rootlets, and the tap roots, crowns, and lower stems were necrotic and turned dark brown to black. Rotted roots were colonized heavily by fungal oospores. Many affected plants wilted and died before flowering. A Phytophthora sp. was isolated consistently from the necrotic roots and crowns of symptomatic white lupins. The same fungus also was isolated from the necrotic root tissues of the other indigenous lupin species. Isolates of the fungus from diseased white lupins were homothallic and produced oospores rapidly and abundantly on corn meal and V8 agars. Antheridia were amphigynous, and aplerotic oospores ranged from 22 to 32 µm (average 27 µm). Nonpapillate, ovoidobpyriform sporangia were produced only in water on simple sympodial sporangiophores. Cultures on V8 agar grew at 5 to 30°C (optimum ≈25°C). The species was identified as Phytophthora erythroseptica Pethybr. based on morphology of oospores, sporangia, and other cultural characteristics (1). Koch's postulates were fulfilled by planting seeds of white lupin cv. Multulupa in sterile potting soil infested with a blended culture on V8 agar from a white lupin isolate of P. erythroseptica and reisolating the fungus after 28 days from lesions that developed on the roots and crowns of inoculated plants incubated in a greenhouse at 16 to 26°C. The fungus was not isolated from white lupins seeded in potting soil inoculated with sterile V8 agar. In pathogenicity tests, two isolates of P. erythroseptica from white lupins caused severe symptoms on the roots and crowns of inoculated white lupin cv. Multulupa similar to those observed on white lupins naturally infected in field trials. These isolates also caused root and crown rots on inoculated L. luteus and L. angustifolius. The fungus did not infect the roots or crowns of tarwi (L. mutabilis cv. SCG 20), alfalfa (Medicago sativa cv. Moapa), bean (Phaseolus vulgaris cv. Contender), chickpea (Cicer arietinum cv. Blanco Lechoso), faba bean (Vicia faba cv. Arboleda), lentil (Lens culinaris cv. local), pea (Pisum sativum cv. Lancet), soybean (Glycine max cv. Akashi), or subterranean clover (Trifolium subterraneum cv. Seaton-park). The tests were repeated, and the results were similar. This is the first report of P. erythroseptica infecting Lupinus spp. References: (1) D. C. Erwin and O. K. Ribeiro. 1996. Phytophthora Diseases Worldwide. The American Phytopathological Society, St. Paul, MN. (2) B. Valdés et al. 1987. Flora Vascular de Andalucía Occidental. Ketres, Barcelona, Spain.

A Vascular Wilt of Turnsole Caused by Fusarium oxysporum.

Turnsole (Chrozophora tinctoria) is a common spring-summer weed in chickpea (Cicer arietinum) and other dry-land crop production areas in southern Spain. Under field conditions, this weed often develops a general wilt and eventual death associated with a vascular discoloration of stems and roots. Diseased turnsole plants frequently occurred together with chickpea plants affected by Fusarium wilt caused by Fusarium oxysporum f. sp. ciceris, a major disease of chickpea crops in southern Spain (1). Isolations from roots, stems and leaf petioles of turnsole plants consistently yielded F. oxysporum, and it was morphologically similar to F. oxysporum f. sp. ciceris. To test the pathogenicity of this fungus, germinated and previously surface-sterilized seeds of turnsole and chickpea cultivar Blanco Lechoso were planted in a greenhouse soil mixture artificially infested with four isolates of F. oxysporum from turnsole and two isolates of F. oxysporum f. sp. ciceris, one of them inducing the wilt syndrome and the other causing yellowing (1). Pathogenicity tests were conducted following the standard inoculation method used for F. oxysporum in chickpea (1). Inoculated and control plants were maintained in a greenhouse at 15 to 30°C. Isolates of F. oxysporum from turnsole caused wilt symptoms and death of turnsole plants within 2 months, but chickpea isolates did not affect turnsole. Conversely, chickpea plants were affected only by the two isolates of F. oxysporum f. sp. ciceris from chickpea. All diseased chickpea and turnsole plants exhibited typical vascular discoloration. F. oxysporum was consistently reisolated from the vascular tissues of roots, stems, and leaf petioles of affected plants. Based on these results, the fungus causing wilt of turnsole was identified as a forma specialis of F. oxysporum different from the chickpea wilt pathogen. Since the Fusarium wilt diseases of turnsole and chickpea are caused by different pathogens, the occurrence of F. oxysporum causing wilt of turnsole in the field can not be used to forecast Fusarium wilt of chickpea, but it may be considered as a potential biocontrol agent of this weed under field conditions. This is the first report of F. oxysporum causing wilt of turnsole. Reference: (1) A. Trapero-Casas and R. M. Jiménez-Díaz. Phytopathology 75:1146, 1985.

Phenology of Didymella rabiei Development on Chickpea Debris Under Field Conditions in Spain.

ABSTRACT The development of Didymella rabiei on debris of naturally infected chickpea was investigated in four chickpea-growing areas with different climatic conditions in Spain during 1987 to 1992. D. rabiei extensively colonized chickpea debris and formed pseudothecia and pycnidia. Differentiation of pseudothecial initials occurred regularly across experimental locations by November, 1 month after placement of debris on the soil. Ascospore maturation occurred mainly from late January to late March, depending on location and year. Maximum ascospore discharge from sampled debris pieces placed under suitable environmental conditions occurred 2 to 4 weeks after ascospore maturation, after which ascospore release decreased sharply. Pseudothecia were exhausted, due to ascospore discharge, by the beginning of summer. New asci did not develop in empty pseudothecia and no pseudothecia formed in tissues after the first season. Ascospore maturation and liberation in cooler locations were more uniform and occurred later compared to maturation in warmer locations. Also, production of asci and ascospores per pseudothecium was much higher in cooler than in warmer locations. A similar relationship was found for density of pseudothecia and pycnidia and conidia production per pycnidium. The percentage of mature pseudothecia increased according to the logistic model, with the cumulative number of Celsius degree days calculated by computing the mean of the maximum and minimum daily air temperatures on rainy days from the date of debris placement on the soil. There were significant differences among model parameter estimates between cooler and warmer locations, but minor differences were found among parameters for locations with similar environmental conditions. There was an inverse linear relationship between the average temperature during the period of pseudothecia maturation and the number of asci produced per pseudothecium.

First Report of Phytophthora megasperma and Pythium irregulare As Olive Tree Root Pathogens.

Several species of the genus Phytophthora are associated with root rot and trunk cankers in olive trees (Olea europaea L.). Among them, Phytophthora megasperma has been cited as being associated with olive root rots in Greece (1). Unidentified species of Pythium and Phytophthora have also been associated with olive tree root rots in the United States. However, the status of P. megasperma and Pythium spp. as olive tree root pathogens has remained unclear. Following a 5-year period of severe drought in southern Spain, autumn-winter rainfall rates in 1996 to 1997 steadily increased in both quantity and frequency. Under these unusually wet conditions, olive trees remained waterlogged for several months. During this period, we observed foliar wilting, dieback, and death of young trees, and later found extensive root necrosis. In 46 of 49 affected plantations surveyed, P. megasperma was consistently isolated from the rotted rootlets, particularly in young (<1- to 10-year-old trees) plantations. This fungus was not detected on plant material affected by damping-off from several Spanish olive tree nurseries. The opposite situation occurred with P. irregulare. This species was not associated with rotted rootlets in the field. In contrast, it was consistently isolated from necrotic rootlets from young olive plants affected by damping-off. These plants were grown in a sand-lime-peat soil mixture under greenhouse conditions and showed foliar wilting and extensive necrosis of the root systems. Pathogenicity tests were conducted with several isolates of P. megasperma and P. irregulare on 6-month-old rooted cuttings of olive, under both weekly watering and waterlogged conditions. Under waterlogged conditions, both fungal species produced extensive root necrosis 2 weeks after inoculation that resulted in wilting of the aerial parts and rapid plant death. Waterlogged control plants remained without foliar symptoms but a low degree of root necrosis was recorded. In addition, under weekly watering conditions, plants inoculated with either species showed some degree of root rot but foliar symptoms were not evident. No differences in pathogenicity were observed within the Phytophthora or Pythium isolates. Reference: (1) H. Kouyeas and A. Chitzanidis. Ann. Inst. Phytopathol. Benaki 8:175, 1968.