Ecology and biology of Rhamphicarpa fistulosa, a new parasitic weed of Rain-fed Rice (Oryza sativa) in sub-Saharan Africa
Kabiri, Stella - \ 2017
Wageningen University. Promotor(en): N.P.R. Anten, co-promotor(en): L. Bastiaans; J. Rodenburg. - Wageningen : Wageningen University - ISBN 9789463436052 - 130
oryza sativa - parasitic weeds - crop ecology - orobanchaceae - weed control - africa south of sahara - oryza sativa - parasitaire onkruiden - gewasecologie - orobanchaceae - onkruidbestrijding - afrika ten zuiden van de sahara
Rice is an important staple food crop in Africa. The increasing scarcity of agricultural land has driven rice growers to expand into marginal areas that have natural infestations of Rhamphicarpa fitulosa. In return, R. fistulosa has increasingly become a serious problem to rice production in sub-Saharan Africa. To date, the understanding of the ecology and biology of the species and its dependence and effects on a host, is rather limited. The discrepancy between the emergence of this weed problem and the virtual absence of knowledge on the weed species motivated the study presented in this thesis.
In a field survey in Tanzania, Striga asiatica was observed in higher lying and drier fields, while R. fistulosa was observed in the lower lying wetter fields. Experiments confirmed that S. asiatica is favoured by free-draining soils and R. fistulosa by water-logged soils. These results imply that changes in climate, specifically moisture regimes, will be crucial for the future prevalence of both parasitic weed species. In a second investigation, I found that daylight and completely saturated soil conditions were prerequisites for germination, demonstrating that R. fistulosa is a typical species of environments with fluctuating water levels. Neither root exudates collected from rice host plants, nor the synthetic germination stimulant GR24, triggered germination of R. fistulosa seeds. Host plant presence resulted in a 3.7 times higher seed production rate and a 15% larger average seed size. The absence of a host recognition mechanism at the germination stage suggests that either the regulation of germination through light and soil moisture is near optimal, or that for this parasitic plant species an opportunistic germination strategy is superior. In a third study, I observed that infection by R. fistulosa led to significant reductions in leaf photosynthetic rate, stomatal conductance, the quantum efficiency of PSII (ΦPSII) and chlorophyll content of rice. In addition, there was a 19-32% negative deviation of the linear relationship between quantum yield of CO2 assimilation (ΦCO2) and quantum efficiency of PSII (ΦPSII) of infected plants in comparison to un-infected plants. This indicated a parasite induced influence on the photochemical process of the host. Furthermore, there was a considerable time lag between the parasite’s gains in growth and the reduction of host photosynthesis. The reduction in host growth, coincided with suppression of host photosynthesis. This indicates that R. fistulosa affects host growth by first extracting assimilates and making considerable gains in growth, before it affects the host photosynthesis. In the final investigation, I examined how the interaction between host plant and parasite influenced growth and (re)production of R. fistulosa and rice. Infection by R. fistulosa increased root:shoot ratio and decreased plant height, leaf area and tiller number of rice. Reductions in light interception of the host were followed by reductions in light use efficiency, causing 22-71% losses in host plant biomass and 78-100% losses in host kernel production. Parasitism eventually caused a complete standstill of host plant growth, while the parasite managed to gradually increase its share of the total host plant-parasite biomass up to 50-82%. This implies that ultimately the host plant was producing solely for the sake of the parasite.
In a final chapter, I discuss the implications of my findings for the future expansion of this parasitic weed, specifically in light of climate change. I also discuss how the divergent ecology and biology of R. fistulosa is likely to influence the effectiveness of measures that are currently applied to manage Striga spp. I argue that more than the current attention needs to be paid to R. fistulosa, specifically for the problems it causes to the rice sector in sub-Saharan Africa.
Rhamphicarpa fistulosa, a widespread facultative hemi-parasitic weed, threatening rice production in Africa
Rodenburg, J. ; Morawetz, J.J. ; Bastiaans, L. - \ 2015
Weed Research 55 (2015). - ISSN 0043-1737 - p. 118 - 131.
sub-saharan africa - fed lowland rice - phylogenetic-relationships - rhinanthus-minor - scrophulariaceae - vegetation - orobanchaceae - management - haustoria - habitats
Rhamphicarpa fistulosa is a facultative hemi-parasitic plant of the Orobanchaceae family, adapted to wet soils. Apart from tropical Australia, it is only found in sub-Saharan Africa, where it is considered a minor weed in cereal crops such as rice. Due to this status, the species has received only sporadic attention. Recent field observations and encounters with rice farmers in several African countries showed that R. fistulosa is, however, a more serious and increasing production constraint than previously thought. Results from a systematic literature review and a global herbarium study support this. The species has a broad distribution over Africa (at least 35 countries from Madagascar to Senegal and from Sudan to South Africa) and a wide range in altitude (0–2150 m a.s.l.) and environment (waterlogged swamps to moist free-draining uplands). Rhamphicarpa fistulosa is relatively independent and persistent because of the presumably wide host range, the facultative nature of its parasitism and its prolific seed (estimated 100 000 seeds m-2 under moderate infestation levels). Finally, R. fistulosa causes severe yield losses (average 60%) and high regional annual economic losses (estimated US $175 million), while effective control options are scant and awareness of the species among important R&D stakeholders is almost absent. An integrated approach is advocated to assist the rice sector to reduce current R. fistulosa-inflicted losses and to prevent further spread of the species into new areas.
Nieuwe inzichten in de interactie tussen sorghum en het parasitaire onkruid Striga hermontica
Ast, A. van - \ 2006
Gewasbescherming 37 (2006)6. - ISSN 0166-6495 - p. 275 - 278.
striga hermonthica - parasitaire planten - striga - orobanchaceae - waardplanten - sorghum - graansoorten - ziektebestrijdende teeltmaatregelen - onkruidbestrijding - cultuurmethoden - bodemvruchtbaarheid - gewasbescherming - afrika - striga hermonthica - parasitic plants - striga - orobanchaceae - host plants - sorghum - cereals - cultural control - weed control - cultural methods - soil fertility - plant protection - africa
Striga hermonthica (Del.) Benth. is een parasitaire plant uit de Orobanchaceae familie. De soort komt van oorsprong voor in Afrika en hecht zich aan de wortels van belangrijke voedselgewassen als maïs, sorghum, gierst en rijst. In grote delen van Afrika heeft Striga zich ontwikkeld tot de belangrijkste groeireducerende factor. Veelvuldig is waargenomen dat de problemen met Striga toenemen wanneer de bodemvruchbaarheid afneemt
Management of broomrape (Orobanche cernua) in tobacco (Nicotiana tabacum)
Dhanapal, G.N. - \ 1996
Agricultural University. Promotor(en): P.C. Struik; M. Udayakumar; S.J. ter Borg. - S.l. : Dhanap␁al - ISBN 9789054855712 - 183
parasitaire planten - epifyten - nicotiana - tabak - orobanchaceae - gewasbescherming - plagenbestrijding - ziektebestrijding - parasitic plants - epiphytes - nicotiana - tobacco - orobanchaceae - plant protection - pest control - disease control
Tobacco is an important commercial crop in India. India is the third largest tobacco producing country in the world. Tobacco is cultivated in an area of 0.428 million ha. Non- Virginia tobaccos such as bidi tobacco constitute about 65% of the total tobacco area in the country.
Broomrape (Orobanche cernua) is a debilitating holoparasitic weed in all tobacco growing areas in India, with a devastating effect on the crop. In India, yield loss in tobacco ranges from 30 - 70%; at present hand weeding is the only practice in India applied to control the parasite.
With this background, several field and laboratory experiments were conducted in Karnataka State, Southern India, to study the germination biology and to develop a suitable method to induce the germination of the parasite, and to develop a technology by integrating agronomic and chemical approaches to control the parasite at different phases.
The germination phase of the parasite is a critical period. The seed bank of the parasite cae be reduced by stimulating the germination through chemicals, natural host stimulants or both. GR24 (a strigol analogue) at 1.0 and 0.1 ppm, was the standard to assess potential germination. Of the other chemicals, gibberellic acid at 10 and 20 ppm was most effective. The stimulating effects of host plants were significant even when GR24 was applied. Suicidal germination of the parasitic seeds triggered by growing trap crops reduced the weed population and the growth of the host plants was hastened due to green manuring effect of trap crops. Therefore, including a trap crop in the rotation may reduce the problem. Sunhemp (Crotalaria juncea L.) and greengram (Vigna radiata L.) are promising trap crops in a cropping system containing bidi tobacco in areas where tobacco is grown in a long growing season.
Chemical control by (systemic) herbicides is also an option. Maleic hydrazide (MH) reduced broomrape spikes at 0.25 - 0.75 kg a.i./ha applied at 30 or 40 days after transplanting (DAT) tobacco. Higher tobacco yields were obtained with 0.25 kg a.i./ha MH, which was on par with the hand weeding treatment both in "infested" and "non- infested" tobacco plants. Higher concentrations of MH were toxic to tobacco crop. Glyphosate at 0.50 kg a.i./ha applied at 60 DAT and imazaquin at 0.01 kg a.i./ha applied at 30 DAT reduced the broomrape population by almost 80% and increased tobacco leaf dry weight by more than 40% compared to the control treatment. Imazapyr and EPTC were less effective.
Swabbing natural plant oils killed the bud and stem parts of the parasite by suffocation. Neem, coconut and sunflower oils showed quick knock-down effects in killing the bud part, whereas neem oil did not kill the stem part of the parasite. Niger, castor and mustard oils appeared to be (somewhat) less effective.
In general, there is a negative linear relation between broomrape infestation and tobacco yield, with a very large (negative) regression coefficient.
No single method is effective in controlling the parasite. The seed bank of the parasite should be minimized in a phased manner by integrating cultural and chemical methods of control. Therefore, an integrated management strategy is the best perspective to control broomrapes in a crop wherever it is problematic.
Key words: bidi tobacco, broomrape, chemical control, Crotalaria juncea, gibberellic acid, germination stimulants, GR24, herbicides, integrated weed control, natural plant oils, Orobanche cernua, parasitic weed, suicidal germination, trap crop, Vigna radiata.