Cucurbits (Cucurbitaceae; Cucumis spp., Cucurbita spp., Citrullus spp.)

The Cucurbitaceae is a remarkable plant family, deserving of attention because of its economic, aesthetic, cultural, medicinal, and botanical significance. In the Old and New Worlds, cucurbits have been associated with human nutrition and culture for more than 12,000 years (Brothwell and Brothwell 1969; Lira-Saade 1995). Thus, the Cucurbitaceae, along with the Brassicaceae and Asteraceae, can be considered families of extraordinary importance to humans, and they follow cereals and legumes in their economic significance to human economy (Whitaker and Davis 1962; Nayar and More 1998)

Distribution and ecology of wild lettuces Lactuca serriola L. and Lactuca virosa L. in central Chile

Wild lettuces (Lactuca L.) may provide valuable genetic resources for crop breeding, but are also significant invasive weeds. Monitoring populations of these species is important, therefore, both to inform genetic resource conservation efforts as well as for non-native plant species control. We explored the occurrences, distributions, and characteristics of populations of wild Lactuca species in central Chile through field surveys in 2016 and 2017, significantly adding to the available information on these species in the region. We documented two species - prickly lettuce (Lactuca serriola L.) and opium (bitter) lettuce (Lactuca virosa L.) in 204 localities. Occurrence only of L. serriola was recorded at 166 sites, only L. virosa at 21 sites, and both at 17 sites. Prickly lettuce was observed equally in urban areas and along transport corridors outside cities. Population sizes varied from a few plants to hundreds of individuals. Opium lettuce was recorded most frequently along roads outside cities, with population sizes of several individuals to a dozen. Species succession in different elevational gradients was observed along three roads: R 60 (Los Andes – Portillo), G-27 (Cajón Maipú), and 115 (Lago Colbún – Lago del Maule). These observations indicate that: i) both allochthonous (Euroasian) wild Lactuca species occur and are able to regenerate in central Chile; ii) L. serriola forms dense populations in urbanized areas; iii) both species can expand along transport corridors to high elevations; iv) the spread of L. virosa and persistence of dense populations in elevations above 2,000 m a.s.l. prove the invasiveness of this species in extreme climates; v) both species should be monitored (and treated) both in urbanized and agricultural areas, as well as in unique local mountainous areas

Phenotypic and histological expression of different genetic backgrounds in interactions between lettuce, wild Lactuca spp., L-sativa x L-serriola hybrids and Bremia lactucae

Phenotypic and histological responses of cultivated lettuce (Lactuca sativa) and wild relatives L. saligna, L. virosa as well as interspecific crosses derived from L. sativa x L. serriola to two races of Bremia lactucae (CS2, CS9) were investigated. With the exception of L. sativa genotypes, all accessions and hybrids expressed incomplete or complete resistance to both pathogen races, with slight differences at seedling and adult plant stages, respectively. Histological features of the interactions (development of pathogen infection structures and host hypersensitive response to attempted infection) were studied on leaf discs 48 h after inoculation. Interactions with similar phenotypic expression of resistance were characterized by significant variation in rate of development of pathogen infection structures and hypersensitive reactions. Differences found within eight Lactuca spp. accessions and hybrids challenged by two distinct pathogen races are interpreted and discussed

Razširjenost in ekologija divjih vrst solate Lactuca serriola L. in Lactuca virosa L. v centralnem Čilu

Wild lettuces (Lactuca L.) may provide valuable genetic resources for crop breeding, but are also significant invasive weeds. Monitoring populations of these species is important, therefore, both to inform genetic resource conservation efforts as well as for non-native plant species control. We explored the occurrences, distributions, and characteristics of populations of wild Lactuca species in central Chile through field surveys in 2016 and 2017, significantly adding to the available information on these species in the region. We documented two species - prickly lettuce (Lactuca serriola L.) and opium (bitter) lettuce (Lactuca virosa L.) in 204 localities. Occurrence only of L. serriola was recorded at 166 sites, only L. virosa at 21 sites, and both at 17 sites. Prickly lettuce was observed equally in urban areas and along transport corridors outside cities. Population sizes varied from a few plants to hundreds of individuals. Opium lettuce was recorded most frequently along roads outside cities, with population sizes of several individuals to a dozen. Species succession in different elevational gradients was observed along three roads: R 60 (Los Andes – Portillo), G-27 (Cajón Maipú), and 115 (Lago Colbún – Lago del Maule). These observations indicate that: i) both allochthonous (Euroasian) wild Lactuca species occur and are able to regenerate in central Chile; ii) L. serriola forms dense populations in urbanized areas; iii) both species can expand along transport corridors to high elevations; iv) the spread of L. virosa and persistence of dense populations in elevations above 2,000 m a.s.l. prove the invasiveness of this species in extreme climates; v) both species should be monitored (and treated) both in urbanized and agricultural areas, as well as in unique local mountainous areas

First detection of tomato powdery mildew caused by Oidium neolycopersici in South Africa

Oidium neolycopersici has a world-wide distribution causing severe epidemics mainly on greenhouse tomatoes. Currently, only Leveillula taurica has been reported on tomato from South Africa. However, another powdery mildew species on tomato was found recently. Based on morphological comparison and molecular analysis, its identity was confirmed as O. neolycopersici. The possible means of introduction and other aspects of this finding are discussed

Cucurbits (Cucurbitaceae; Cucumis spp., Cucurbita spp., Citrullus spp.)

The Cucurbitaceae is a remarkable plant family, deserving of attention because of its economic, aesthetic, cultural, medicinal, and botanical significance. In the Old and New Worlds, cucurbits have been associated with human nutrition and culture for more than 12,000 years (Brothwell and Brothwell 1969; Lira-Saade 1995). Thus, the Cucurbitaceae, along with the Brassicaceae and Asteraceae, can be considered families of extraordinary importance to humans, and they follow cereals and legumes in their economic significance to human economy (Whitaker and Davis 1962; Nayar and More 1998).This is a chapter from Genetic Resources, Chromosome Engineering, and Crop Improvement: Vegetable Crops 3 (2007): 271. </p

Resurgence of Pseudoperonospora cubensis: the Causal Agent of Cucurbit Downy Mildew

The downy mildew pathogen, Pseudoperonospora cubensis, which infects plant species in the family Cucurbitaceae, has undergone major changes during the last decade. Disease severity and epidemics are far more destructive than previously reported, and new genotypes, races, pathotypes, and mating types of the pathogen have been discovered in populations from around the globe as a result of the resurgence of the disease. Consequently, disease control through host plant resistance and fungicide applications has become more complex. This resurgence of P. cubensis offers challenges to scientists in many research areas including pathogen biology, epidemiology and dispersal, population structure and population genetics, host preference, host-pathogen interactions and gene expression, genetic host plant resistance, inheritance of host and fungicide resistance, and chemical disease control. This review serves to summarize the current status of this major pathogen and to guide future management and research efforts within this pathosystem