Infection time and density influence the response of sorghum to the parasitic angiosperm Striga hermonthica

Abstract

Two cultivars of sorghum (CSH-1 and Ochuti) were grown in the presence and absence of the root hemiparasite Striga hermonthica in uniform conditions in the field in Kenya, Africa. S. hermonthica had a marked influence on growth and photosynthesis of ' CSH-1 ' ; however, ' Ochuti ' showed a less severe response to infection and tolerance of the parasite. The variation in genotype response might be partly explained by later attachment of the parasite and a lower level of infection. Laboratory studies were used to determine the importance of both variables in determining host response to infection. Early infection by S. hermonthica had a more negative effect on the host than late infection. The level of parasite biomass supported by the host also influenced host productivity but the relationship was nonlinear. Low degrees of parasite infection had a proportionately much greater effect on host grain weight than at greater parasite loading. Early infection of ' Ochuti ' in laboratory conditions resulted in lower stem dry weight than in uninfected plants but not in smaller total plant biomass or lower rates of photosynthesis.In conclusion, the time of parasite attachment affected host performance and might explain much of the variation in host sensitivity both within and between studies. The level of parasite infection affected host performance to a lesser extent. In addition, late attachment and low levels of infection might have implications for control management strategies.

Natural variation of rice strigolactone biosynthesis is associated with the deletion of two MAX1 orthologs

“…1A). The later establishment of infection in Azucena likely explains the higher tolerance to Striga, similar to what was observed in sorghum, where tolerant varieties generally exhibit later Striga emergence (40). Intriguingly, Striga postattachment resistance mapped to the same position on chromosome 1 as the QTL discussed in the present work (near marker C1370) in a cross between Nipponbare and Kasalath (21), with the Nipponbare allele conferring greater resistance (41).…”

Characterization of host tolerance to Striga hermonthica

“…Koskela et al (2002) reported a similar relationship between parasite infection level and host damage for the holoparasite Cuscuta europaea parasitizing on Urtica dioica. Gurney et al (1999) found a negative and exponential relationship between yield and parasite load for Striga hermonthica parasitizing on sorghum, where parasite load was expressed as Striga dry weight. These findings do not necessarily contradict findings of the current study.…”

“…Determination of the relative yield loss already requires the presence of Striga-free control plots adjacent to Striga infested plots (e.g. Gurney et al, 1999;Rodenburg et al, 2005). Control plots in the field can be created by use of methyl bromide (e.g.…”

“…Control plots in the field can be created by use of methyl bromide (e.g. Gurney et al, 1999) or ethylene injections (e.g. Bebawi et al, 1985;Bebawi & Eplee, 1986) which are both rather expensive and laborious.…”

“…Such a correction requires that the relation between Striga infection level and yield loss is known. Studies in which the biomass of the parasite was used as infection measure suggest that the relation between Striga infection level and yield loss is non linear and characterized by a diminishing slope with increasing infection level (Gurney et al, 1999(Gurney et al, , 2000. Whether this type of relation also holds for the relation between Striga number and yield loss is not yet clear.…”