The effect of Phelipanche ramosa infection on the quality of tomato fruit

The influence of the root holoparasite Phelipanche ramosa on the physical characteristics and chemical composition of greenhouse-grown tomato fruits was studied over two growing seasons. The presence of the parasite significantly reduced fruit fresh and dry weight, mesocarp thickness, fruit colour, firmness and titratable acidity. The content of reducing sugars, soluble solids, ash and ascorbic acid was also reduced, but the number of seeds per fruit increased with the parasite. Since some of these traits are important determinants of fruit quality from the consumers' point of view, it is clear that P. ramosa infection reduces the marketable value of tomato. The deterioration in fruit quality worsens over time and hence, by inference, with the intensity of the parasite infection.     

Fenugreek root exudates show species-specific stimulation of Orobanche seed germination

Various Orobanche species are weedy and cause severe reduction in the yields of many important crops. The seeds of these parasitic weeds may remain dormant in the soil for many years until germination is stimulated by the release of a chemical signal from a host plant. In order to determine the effects of fenugreek root exudate on the induction of Orobanche crenata, Orobanche ramosa and Orobanche foetida seed germination, root exudate was collected from hydroponically grown fenugreek seedlings. Fractionation patterns obtained from column and thin layer chromatography of the fenugreek root exudate showed a set of metabolites differing in their polarity with stimulatory activity on Orobanche seed germination. The crude root exudate stimulated both O. ramosa and O. crenata seed germination to the same level caused by the synthetic germination stimulant GR24 at 10 mg L^?1. It also stimulated O. foetida seed germination which did not respond to GR24. Active fractions of root exudate stimulated the germination of Orobanche species differentially.     

Effectiveness of ten commercial maize cultivars in inducing Egyptian broomrape germination

Egyptian broomrape (EB), Phelipanche aegyptiaca, is a devastating root parasite, causing enormous crop losses around the world. Maize has the potential to influence the growth of other plants through releasing certain allelochemicals and is able to induce germination of at least three broomrape species. To determine whether maize could be used as a trap crop for EB, 10 maize cultivars were tested for their ability to induce EB germination. The results showed that maize cultivars can induce EB germination, and that germination rates in a cut-root experiment and a hydroponic experiment were consistent. Maize cvs Changcheng 799 and Zhengdan 958 induced the highest EB germination rates, while cvs Luyu 13 and Zhengyu 203 were the least effective. These four maize cultivars were further studied in a pot experiment. Rhizosphere soil, rhizosphere soil extracts, root extracts and shoot extracts from these cultivars were all able to induce EB germination, with cv. Changcheng 799 inducing the highest germination rates. Root extracts generally induced higher germination rates than shoot extracts. It is suggested that Changcheng 799 could be planted as a trap crop for control of EB.     

Resistance to broomrape in wild lentils (Lens spp.)

Orobanche crenata , Orobanche aegyptiaca and Orobanche foetida constitute serious threats to grain legumes in the Mediterranean Basin. Lentil can be severely infected by O. crenata . It can also be damaged although with less virulence by O. aegyptiaca , and can only be slightly infected by O. foetida . Resistance breeding is hampered by scarcity of proper sources of resistance in cultivated lentil and of a reliable and practical screening procedure. A germplasm collection of 23 wild Lens spp. accessions was screened for resistance to O. crenata under field conditions. A wide range of responses was observed, from complete resistance to susceptibility. The higher levels of resistance were observed in accessions of Lens ervoides , Lens odemensis and Lens orientalis . Resistance of selected accessions proved to be mainly because of early hampered tubercle formation, with no observed necrosis of established tubercles. No differences were observed in levels of induction of broomrape germination, but necrosis of broomrape radicles was significant in some cases, particularly in the L. odemensis–O. foetida interaction. Escape because of the reduced root biomass diminishing the chance of contact between host and parasite was also observed in L. odemensis .     

Reproductive behaviour and broomrape resistance in interspecific hybrids of sunflower

Interspecific hybrids and backcross generations between the wild perennial species Helianthus resinosus, Helianthus paucifiorus, Helianthus laevigatus, Helianthus nuttallii ssp. nuttallii T. & G. and Helianthus giganteus, resistant to broomrape (Orobanche cernua) and susceptible inbred lines were obtained to study crossability to cultivated sunflower and the transmission and expression of resistance to this parasitic weed. Conventional crosses with all the species tested were successful except for the crosses with diploid H. giganteus, for which embryo rescue techniques were needed to overcome hybrid incompatibility. Pollen viability and seed set were highest for F₁ hybrids with hexaploid species and lowest for those with the diploid H. giganteus. We evaluated F₁, BC₁F₁, some BC₂F₁ plants and the wild and cultivated parents. The wild species and interspecific hybrids were resistant to broomrape infection except for H. nuttallii, which showed segregation, indicating that the resistance is dominant. The crossability and resistance of F₁, and back-cross generations of species with different ploidy levels indicate that the transfer of broomrape resistance to cultivated sunflower is feasible.     

Genetic differentiation and host preference reveal non‐exclusive host races in the generalist parasitic weed Phelipanche ramosa

We developed 20 microsatellite markers to genotype over 100 populations of the parasitic weed Phelipanche ramosa, which covers a wide host crop and geographic range. A representative core collection of 15 populations was also used in cross‐infestation assays to study host preference during germination, attachment and shoot formation. We observed low genetic differentiation within most of the populations, but high genetic differentiation between populations partitioned into 3 genetic groups with different host preferences and geographic distributions. Genetic group 1 is detected exclusively in western France and on various host crops, notably winter oilseed rape (WOSR) and not hemp. Cross‐infection assays confirmed its incompatibility with hemp and showed its preference for WOSR and tobacco in terms of germination and attachment success. The group 2 populations share a large geographic distribution in France and Europe, low germination success with WOSR and high germination success, attachment success and shoot formation with hemp, tobacco or tomato. The subclades 2a and 2b include most of the French populations in hemp crops in eastern France and in tobacco fields in several European countries respectively. The genetic analyses revealed the potential of the three groups to increase their geographic range in the future. Intermediate genetic groups showed higher intrapopulation diversity and represent potential stocks for new host race emergence. Those findings argue in favour of the existence of host races in P. ramosa and should be considered for appropriate management strategies, notably in breeding programmes for resistance against this parasitic weed.     

Genetic diversity of Orobanche cumana populations from Spain assessed using SSR markers

Orobanche cumana (sunflower broomrape) is found in Spain as an allochthonous species parasitising exclusively sunflower. For many years, it was distributed in the Guadalquivir Valley and Cuenca province, but in recent years, it has spread to new areas. The objective of this research was to study genetic diversity of O. cumana populations from Spain using robust co‐dominant molecular markers. Cluster analysis on a set of 50 populations using 15 microsatellite markers revealed the existence of two distant gene pools, one in Cuenca province and another one in the Guadalquivir Valley. Within each gene pool, both inter‐ and intrapopulation variability were extremely low. This population structure probably reflects a founder effect, with the two genetically distant gene pools deriving from separate introduction events. Different races occurred within the same gene pool, suggesting that current races might have evolved through mutation from a common genetic background. Most of the populations from new areas were identical to the populations from the Guadalquivir Valley. Only a few populations showed larger intrapopulation variation. In these cases, our results suggested the co‐existence of both gene pools within the same population, as well as the occurrence of genetic recombination between them. Genetic recombination between distant gene pools is an important mechanism for creating new variation, which might also have an effect on race evolution. These results will contribute to the establishment of improved crop breeding and management strategies for O. cumana control.