Subject: A Study on Host plant resistance in connection with the parasitic weed Orobanche (broomrape) and the relationship between broomrape ecology and integrated control schemes�

From: [email-masked]
Date: 11 Dec 1996 17:06:58 GMT

A project entitled “A Study on Host plant resistance in connection 
with the parasitic weed Orobanche (broomrape) and the relationship 
between broomrape ecology and integrated control schemes” led by A. 
H. Pieterse of Royal Tropical Institute ( KIT ), The Netherlands, 
in partnership with other scientific institutions in Egypt, Spain, 
Syria, and The Netherlands was carried out under the European Union 
(D.G.XII) STD2 scientific programme.

The objective of this project was to contribute for the development 
of integrated means of control of species Orobanche crenata and O. 
cernua.
Literature reviews on control and germination of Orobanche spp. and 
laboratory, greenhouse and field experiments were carried out 
between 1988 and 1993.
The project was developed following different lines: germination 
ecology; biotype characterisation; population dynamics; effects of 
ammonium fertiliser, soil moisture and sowing date of sunflower on 
Orobanche infestation; interaction between Orobanche and partly 
resistant faba beans cultivars; effectiveness of several herbicides 
in the control of Orobanche; and integrated control considering the 
use of herbicides, fertilisers and dates of sowing.
>From  the results some features are outlined as follows.
Under the line of germination ecology it was observed that final 
germination percentage was maximal within a narrow temperature 
range of 10 - 20ºC or 15 - 20ºC, decreasing rapidly on either side 
of this optimum; at 0ºC and 35ºC no germination occurred. 
Germination rate was highest at 25 - 30ºC, but the seed lots under 
study did not differ with regard to temperature dependence of lag 
time or germination rate.
Optimum temperature for conditioning was in general 15 - 20ºC.
The effect of conditioning at 20ºC during different periods of 
germination was also assessed considering Egyptian and Syrian 
seeds.
The observed seasonal pattern in germinability, in relation to 
rainfall and soil temperature, was largely consistent with the 
results of in vitro experiments, searching for the effect of 
conditioning temperature and conditioning period on germination 
capacity and the development of secondary dormancy.
Moisture and temperature can be considered as the major factors 
regulating induction of dormancy in buried O. crenata seeds.
On the biotype characterisation, four genetic loci were 
interpretable and used for a population-genetic analysis of three 
populations o O. crenata; levels of polymorphism were high. In the 
populations of O. cernua the isoenzyme patterns and its polymorphic 
index differed considerably.
Studies on population dynamics in faba bean fields showed that O. 
crenata seed production was related to the height of the parasite 
and severity of the infection. Early emergence of broomrapes 
produced more seeds than those emerged later. The O. crenata 
seedbank increased every year in the 20 cm depth arable layer until 
it reached approximately 4 million seeds m². Seed viability ranged 
between 53% and 68%, with approximately half of the seeds remaining 
dormant.
In sunflower fields, it appeared that O. cernua seeds were spread 
via sunflower achenes over large distances. Orobanche was found in 
46% of the visited fields, but generally the infestation level was 
relatively low.
Regarding the effect of ammonium fertiliser on O. crenata 
infestation applications of ammonium sulphate produced a reduction 
in the number of shoots.
In relation to the effect of soil moisture on Orobanche 
infestation, dry weights and numbers of host and parasite were 
generally higher under moist than under dry conditions, finding 
which is not in agreement with previous reports.
Considering the effect of sowing date  infestations were less at 
the first than the second or third sunflower sowings and caused 
fewer yield reductions. The duration of the broomrape emergence 
period increased when sowing date was delayed. Since sunflower 
yields were higher at earlier sowing dates, early sowing may be 
recommended for sunflower crops in broomrape infested areas under 
certain climatological conditions.
For the control of Orobanche some herbicide treatments were 
assessed. If pre-emergence treatments of imazapyr were well 
tolerated by faba beans, the effect on Orobanche was poor and 
depending on the type of soil. Post-emergence treatments provided 
good broomrape control without crop injury. Glyphosate effectively 
controlled O. cernua in sunflower crops but yields of treated 
fields were not higher than those of the untreated infested 
control, probably to the fact that glyphosate application to 
sunflower is to a certain extend phytotoxic.
Imazethapyr at 20-40 g/ha, imazapyr at 12.5-25 g/ha and 
chlorsulfuron at 4-6 g/ha controlled O. cernua efficiently without 
crop injury. Imazaquin at 20-40 g/ha, triasulfuron at 4 g/ha, 
CGA-136 at 3 g/ha acetochlor at 4.4 kg/ha and metazaclhor at 2 
kg/ha were less efficient. Imazetabenz at 200-600 g/ha and 
metaclhor at 3.3 were ineffective.
Susceptible cultivars of faba bean collapsed before the end of 
growing season, whereas others (particularly line 402/294) remained 
alive until pod formation was completed. On the basis of the 
results, some lines of faba beans are partially resistant, due to 
some defence mechanism in their roots.

Contract number TS2-A-124

Studies on integrated control included the use of imazethapyr, 
imazapyr and chlorsulfuron applied at crop pre-emergence; the 
products were very effective against O. cernua without causing crop 
fitotoxity. Sowing dates were also considered; but if with the 
legumes, potential crop yields and parasite infestation increased 
when the sowing date was fixed at an earlier time, the opposite 
occurred with sunflower.
Other experiments with herbicides showed that the recommended 
herbicide treatments for broomrape control varied with cropping 
systems and environmental conditions.

The 3rd International Workshop on Orobanche was held in The 
Netherlands (8-12 November 1993) where 90 papers were presented.

Several publications and three Ph D thesis were also results of the 
project.

For further information please contact:

A. H. Pieterse
Royal Tropical Institute (KIT)
Mauritskade 63, 1092 AD Amsterdam, The Netherlands

Telephone (20) 5688307
Telex / Fax (20) 5688444  15080 KITNL

Contract number TS2-A-124