Management of chili pepper root rot and wilt (caused by Phytophthora nicotianae) by grafting onto resistant rootstock

Root rot and plant wilting caused by Phytophthora nicotianae is a severe disease of chili pepper (Capsicum annuum L.) in open fields and under greenhouse production in Tunisia. Chili pepper grafting for disease manage- ment is attracting increased interest in recent years. Using the tube grafting technique, different compatible scion/rootstock combinations were obtained with the wild-type pepper SCM334 and the local chili pepper cultivars ‘Beldi’ and ‘Baker’. SCM334 was resistant to P. nicotianae, while the cultivars Beldi and Baker were susceptible. Plant inoculations were performed with P. nicotianae zoospores, and severity of root rot was rated 30 days post- inoculation using a 0 (healthy plant) to 5 (dead plant) severity score. On SCM334 rootstock and with ‘Beldi’ or ‘Baker’ scions, the intensity of root rot was very low (mean score 0.1–0.2) and plants were healthy. However, with Baker or Beldi rootstocks and SCM334 scions, root rot was severe (mean score 3.1–4.6), leading to high numbers of wilting and dead plants. This severe root rot was similar to that observed on non-grafted plants of ‘Baker’ and ‘Beldi’ inoculated with the pathogen. Under greenhouse conditions, measurements of agronomic characters indicated non-consistent improvement of these features on the scion cultivar when SCM334 was the rootstock. Since plant foliage is not attacked by this pathogen, these results show that susceptible chili pepper scions grafted onto SCM334 rootstocks could be used for root rot management and improvement of pepper yields in P. nicotianae infested soils

Evaluation of Seven Essential Oils as Seed Treatments against Seedborne Fungal Pathogens of Cucurbita maxima

: Essential oils are gaining interest as environmentally friendly alternatives to synthetic fungicides for management of seedborne pathogens. Here, seven essential oils were initially tested in vivo for disinfection of squash seeds (Cucurbita maxima) naturally contaminated by Stagonosporopsis cucurbitacearum, Alternaria alternata, Fusarium fujikuro, Fusarium solani, Paramyrothecium roridum, Albifimbria verrucaria, Curvularia spicifera, and Rhizopus stolonifer. The seeds were treated with essential oils from Cymbopogon citratus, Lavandula dentata, Lavandula hybrida, Melaleuca alternifolia, Laurus nobilis, and Origanum majorana (#1 and #2). Incidence of S. cucurbitacearum was reduced, representing a range between 67.0% in L. nobilis to 84.4% in O. majorana #2. Treatments at 0.5 mg/mL essential oils did not affect seed germination, although radicles were shorter than controls, except with C. citratus and O. majorana #1 essential oils. Four days after seeding, seedling emergence was 20%, 30%, and 10% for control seeds and seeds treated with C. citratus essential oil (0.5 mg/mL) and fungicides (25 g/L difenoconazole plus 25 g/L fludioxonil). S. cucurbitacearum incidence was reduced by ~40% for plantlets from seeds treated with C. citratus essential oil. These data show the effectiveness of this essential oil to control the transmission of S. cucurbitacearum from seeds to plantlets, and thus define their potential use for seed decontamination in integrated pest management and organic agriculture

The occurrence of two species of Entomophthorales (Enthomophthoromycota), pathogens of <em>Sitobion avenae</em> ans <em>Myzus persicae</em> (Hemiptera: Aphididae), in Tunesia

The natural occurrence of entomophthoralean fungi pathogenic towards aphids on cereal and potato crops was investigated in the years 2009, 2010, and 2011. Infected aphids were sampled in three bioclimatic zones in Tunisia (Beja, Cap bon, and Kairouan) and fungal species were determined based on morphological characters such as shape, size, and number of nuclei in the primary conidia. Polymerase Chain Reaction (PCR) on the internal transcribed spacer 1 region (ITS1) was used to verify morphological determination. Both methods gave consistent results and we documented for the first time the natural occurrence of two fungal species from the order Entomophthorales (phylum Entomophthoromycota), Pandora neoaphidis and Entomophthora planchoniana. Both fungi were recorded on the aphid species Sitobion avenae and Myzus persicae on barley ears and potato leaves, respectively. Moreover, natural mixed infections by both species (P. neoaphidis and E. planchoniana) were documented on the target aphids. This investigation provides basic information of entomopathogenic fungi infecting economically important aphids in Tunisia

Morphological and Molecular Identification of Seedborne Fungi in Squash (Cucurbita maxima, Cucurbita moschata).

Squash is one of the most important crops of tropical and temperate regions, and it can be affected by several fungal pathogens. Most of these pathogens infect the seeds, which become an efficient vehicle to disperse seedborne pathogens over long distances, with consequent severe crop losses. The main objective of this study was the identification of the principal seedborne fungi in seeds extracted from 66 samples of asymptomatic and symptomatic squash fruit (Cucurbita maxima, Cucurbita moschata) collected in two countries, Tunisia and Italy. The symptoms of fruit decay were identified and classified according to lesion size. Following the blotter test, 14 fungal species were detected from the seeds. Seedborne fungi were identified in all fruit samples tested, including asymptomatic fruit. The most frequent fungi from Tunisian seeds were Alternaria alternata (25.1%), followed by Stagonosporopsis cucurbitacearum (24.6%), Fusarium solani (16.6%), Rhizopus stolonifer (13.3%), F. fujikuroi (7.8%), Albifimbria verrucaria (3.3%), and Stemphylium vesicarium (2.3%). For the fruits from Italy, the most frequently identified fungal species in seed samples were Alternaria alternata (40.0%), followed by F. fujikuroi (20.8%), Stemphylium vesicarium (3.0%), and Curvularia spicifera (2.1%). Morphological identification was confirmed by molecular diagnosis using the available species-specific primers. Furthermore, specific primers were designed to identify Albifimbria verrucaria, Paramyrothecium roridum, and Stemphylium vesicarium. Application of seed-health testing methods, including such conventional and molecular diagnostic tools, will help to improve seed quality and crop yields

Relationship between epistasis and aggressiveness in resistance of pepper (Capsicum annuum L.) to Phytophthora nicotianae

This study evaluated the types of gene action governing the inheritance of resistance to Phytophthora nicotianae necrosis in populations derived from two crosses involving two susceptible (Beldi and Nabeul II) and one resistant (CM334) cultivars of pepper (Capsicum annuum L.). Populations, composed of Pr, Ps, F1 , F 2 , BC 1 Pr, and BC 1 Ps generations, were inoculated with six P. nicotianae isolates. Generation means analysis indicated that an additive-dominance model was appropriate for P. nicotianae isolates Pn Ko1 , Pn Ko2 and Pn Kr1 , which showed low aggressiveness in the two crosses. For the more aggressive isolates Pn Bz1 , Pn Bz2 and Pn Kr2 , epistasis was an integral component of resistance in the two crosses. The presence of epistasis in the resistance of pepper to P. nicotianae was dependent on the level of aggressiveness of the isolates. Selection in pepper with less aggressive isolates was efficient, but not with more aggressive isolates; on the other hand, selection with more aggressive isolates was more stable. The minimum number of genes controlling resistance was estimated at up to 2.71. In the majority of cases, the additive variance was significant and greater than the environmental and dominance variance

Phytophthora nicotianae diseases worldwide: new knowledge of a long-recognised pathogen

Phytophthora nicotianae was first isolated from tobacco at the end of the 19th century. This organism is now considered as one of the most devastating oomycete plant pathogens, with a recognized host range of more than 255 species over five continents and a wide diversity of climates. The economic losses caused by P. nicotianae are difficult to estimate, because of the diversity of its hosts and ecological niches. For these reasons, this pathogen represents a continuous challenge to plant disease management programmes, which frequently rely solely on the use of chemicals. Phytophthora nicotianae is better adapted than its competitors to abiotic stresses, especially to climate warming. As a result, its importance is increasing. This review illustrates, with some examples, how P. nicotianae currently impacts plant economies worldwide, and how it may constitute more severe threats to agriculture and natural ecosystems in the context of global climate change

Oat crown rust in Tunisia in 2003

Crown rust (Cr), caused by Puccinia coronata f. sp. avenae, is generally considered the most widespread and damaging disease of oat in Tunisia. The most important sources of resistance are based on the Pc genes active as racespecific resistance. Sixteen single gene oat lines were sown in 4 sites. Earlyseeded planting were shown to increase early Cr development (Allagui et al. 2002). The conditions of these sites ranged from humid (Sejnane), to subhumid (Lafareg), to semi-arid (Ariana and Bou Rabia). The oat plants were subjected to Cr natural infections during the 2003 to assess with time the most prevalent Cr pathogenic variability. The differential reactions were determined at the maximum Cr attack being in February for Sejnane, in March for Ariana and in April for Lafareg and Bou Rabia. The five lines Pc40, Pc45, Pc46, Pc50 and Pc54 were heavily infested. Infection types ranged between 3 to 4 for these differentials having on the leaf area medium to large uredinia without chlorosis. Reaction of the seven lines Pc48, Pc51, Pc56, Pc58, Pc59, Pc62 and Pc64 varied between site. The four differentials Pc38, Pc39, Pc52 and Pc68 were resistant at Bou Rabia and Ariana. Of these only Pc39 was susceptible in Sejnane but leaf area covered with large uredinia was small (1 %); at Lafareg both Pc52 and Pc68 were susceptible but with only few uredinia on the leaves (1 % and 5 % respectively). According to the nomenclature of Chong et al (2000), reaction of the differentials indicate the Cr virulence phenotypes prevalent in Tunisia ranged from TFRT at Lafareg, to TJFR at Sejnane, to TDFL at Ariana to TBLM at Bou Rabia. The Pc genes, more resistant to oat Cr in Tunisia, were Pc38, Pc39, Pc52 and Pc68. In previous evaluations carried out in 2000-2002, the lines Pc38, Pc39 and Pc68 were equally resistance (Allagui et al. 2002). However, slow rusting with partial resistance is being now more attractive. The most pathogenic variability rendering many genes ineffective was mainly located in Lafareg and Sejnane. These regions are in the neighborhood of the noth-west tunisinan s mountains having different Rhamnus species but not R.cathartica. Surveys on these Rhamnus species, conducted in 2003, showed for the first time in Tunisia that R.lycioïdes is the aecial host for the sexual stage of oat Cr (Hemmami and Allagui. 2003). The high genetic variability of the Cr virulence in these regions could be linked to the aecidial form found on this R.lycioïdes species. Allagui, M.B. et al. 2002. Ann. De l INRAT 75, 205-221; Chong, J. Et al. 2000. Plant Disease 84, 580-585. Hemmami I, Allagui MB, 2003. Proc. of the 10th National Days on Results of Agronomic Research Nabeul (Tunisia).vokMyynti MTT tietopalvelu

Effectiveness of Several GRAS Salts against Fungal Rot of Fruit after Harvest and Assessment of the Phytotoxicity of Sodium Metabisufite in Treated Fruit

This study evaluates the efficacy of the salts sodium metabisulfite (SMB), ammonium bicarbonate, sodium bicarbonate, and potassium dihydrogen orthophosphate first in vitro against the main postharvest fruit rot fungi, Alternaria alternata, Botrytis cinerea, Penicillium italicum, and Penicillium digitatum. Results showed that 0.2% SMB completely inhibited the mycelium growth of the fungal species. Ammonium bicarbonate and sodium bicarbonate were less effective at 0.2% in inhibiting mycelial growth, ranging from 57.6% to 77.6%. The least effective was potassium dihydrogen orthophosphate. Experiments were also performed in vivo on wounded apples inoculated with the most pathogenic fungus, B. cinerea, and treated with SMB at concentrations of 0.2, 0.5, 1, 2, and 3%, both preventively and curatively. Results based on the decay size showed that SMB, when used as a preventive treatment, had a reduced efficacy, even with the highest concentration. However, this salt proved to be very effective at 0.5% in curative treatment since the decay was completely blocked. Our results suggest that the appropriate concentration of SMB for post-harvest treatment is 0.5% as a curative treatment. On the other hand, the 1% dose induced the onset of phytotoxicity around the wound. To assess the extent of the phytotoxicity reaction, higher concentrations of 1–4% SMB were applied to wounded fruit. Apples and oranges were inoculated or not with B. cinerea and P. digitatum, respectively. Doses of 1–4% induced phytotoxicity in the form of a discolored ring surrounding the wound on the epidermis of the fruit; this phytotoxicity enlarged as the concentration of SMB increased. The phytotoxic features were similar on apples and oranges. The methodological procedure made it possible to carry out a quantitative assessment of SMB phytotoxicity. This method is proposed as an easy-to-use technique for quantitatively estimating the phytotoxicity of antifungal compounds on post-harvest fruit