Evaluation of the synergistic effect of host plant resistance, rhizobial inoculant and trichoderma on orobanche infestation of faba beans (Vicia faba l.) in Southern Tigray, Ethiopia

Broomrape (Orobanche crenata F.) has been seriously limiting faba bean production in northern Ethiopia. As a result there is a need to further enhance faba bean production through the development of management options that can be effectively used in combating the parasitic weed problem. This research was conducted with the objectives of quantify the infestation level of O. crenata and associated yield loss in faba bean fields of south Tigray, Ethiopia, evaluate the synergistic effect of host plant resistance and bio-inoculants on O. crenata naturally infested soils of faba bean and to assess pathogenic fungi associated with O. crenata and test their pathogenicity. A field survey was carried out to assess the distribution and infestation level of O. crenata in south Tigray. Field experiment was conducted by using four faba bean varieties and bio-inoculants of R. legimunosarum and T. harzianum that were applied singly or in combination. Uninoculated plots with neither of the inoculants were included as control. The experiment was arranged in factorial RCBD with three replications. Results revealed the prevalence of O. crenata across the region. The highest prevalence (100%) of O. crenata was recorded in Ofla district while O. crenata incidence and severity were the highest in Adigolo Farmers Association(93 and 6.8 %, respectively). Estimated average faba bean yield loss as a result of O. crenata infestation ranged from 2 to 28 % at the district level while average yield loss was estimated to reach 99% at the field level. Various fungal pathogens were found associated with the roots and stems of the O. crenata plant. F. oxysporum was the dominant species with more than 56% incidence. Inoculation of faba bean with R. leguminosarum and T. harzianum singly or in combination significantly reduced O. crenata infestation as compared to untreated checks. Interactions between bio-inoculants and host variety had no significant effect at all. As compared to local variety, the varieties Hashenge, Walki and Moti reduced the incidence of O. crenata infestation by 74, 11 and 10 %, respectively. Similarly, the severity of O. crenata infestation was reduced by 79% on Hashenge variety, 30% on Walki and 16% on Moti variety. As compared to the negative check (no bio-control) T. harzianum, T. harzianum + R. leguminosarum and R. leguminosarum reduced O. crenata incidence by 11.5%, 8.4% and 7.6%, respectively. The same treatments reduced O. crenata severity by 39, 48, and 35%, respectively. Among the bio-inoculants, T. harzianum + R. leguminosarum treated plots had the highest grain yield (803.50 kg/ha), which was a 27% over the untreated control. The highest level of protection against the parasitic weed was achieved on Hashenge variety, which also meant that the same variety had the best agronomic performance and the highest yield. So based on current findings, we recommend that faba bean variety Hashenge be used in combination with T. harzianum + R. leguminosarum as integrated management option against O. crenata. Further evaluations involving additional faba bean varieties and bioinoculants need to be undertaken under different agro-ecological settings.