It is important to say that there are different standards of what is considered to be a resistant crop. In the lab, the resistant crop is the crop with R-gene. For the government bodies, the resistant crop is the crop with Pf/Pi
In addition to number of galls, reproductive factors are also important in the assessment of resistance or susceptibility of cultivars to root-knot nematodes.
Dear Tarik
i think number and size of galls are important for evaluation of resistance to root -knot nematode.
Best Regard
The number of galls indicates the number of J2 that penetrated the roots and established a feeding site. However, estimating the population of eggs and J2 indicates if the plant allowed the reproduction of the nematodes. It is possible that although the plant is tolerant, allow the nematode to develop enough to form galls but not to complete the life cycle until the reproduction stage. Therefore, I recommend, in addition to the galls count, to make an estimate of the reproduction rate
Reproduction index is important
but any one tell me how can i calculate the Root Gall Index?
Counting the number of galls is a very poor method for the estimation of resistance. First of all the number of J2 is the factor you really need to estimate resistance as they are causing the damage. You have to compare the number of J2 produced on the susceptible variety and the tested resistant one. Galls can be empty on some plants and when they are filled the number is very variable. Estimations using galls therefore are error prone with high variability. The reproductive factor is density dependent, which means it changes with the initial population density. In fact, the proper way is estimating the partial resistance using a model describing the population dynamics. This has been done for potato cyst nematodes on potatoes and is now the official way of testing new potato cultivars in the EU. Recently Teklu et al (2016) also used this method to establish resistance towards Meloidogyne chitwoodi in potatoes and recently sugar beets.
The gall numbers it's one of the parameters, so i suggest to count: Egg masses, juveniles from the roots, juveniles in the soils. Also, the growth parameters can be a criterion to compare with the varieties.
Ahmed H. El-Sappah Yes it's very important and i think that it's just an estimation according to a rating schema (number of gall and their distribution) . for example, Zeck 1971 from 0 to 10.
It is important to say that there are different standards of what is considered to be a resistant crop. In the lab, the resistant crop is the crop with R-gene. For the government bodies, the resistant crop is the crop with Pf/Pi
The galls index, eggs for plant, and second-stage juveniles (J2) are an important criterion.
Criteria used to evaluate resistance levels in plant were gall index, egg mass number, gall number, egg mass index and egg number per gram root.
Hi Zoran, unfortunally resistance is completely independent, has no relation, to yield losses. Resistant potato varieties (100% resistant, eg the H1 gene agans G. rostichiensis) suffer the same yield losses as the susceptible plants without the resistance gene. And that also applies to other plnt - nematode combinations. Resistance is here defined as the decreased ability to repreduce on plants with a resistance gene. Also, 100% resistance is rare. Thats why the term partial resistance is becomming more and more used. Again: Pf/Pi is density dependent and differs even at the same Pi from experiment to experiment as result of the different external conditions in experiments. Check out some quantitative nematology like Plant growth and population dynamics by Schomaker.
- Badges
- Science topic
- Similar topics
- Entomology
- Resistance