Introduction

Nematodes are inoculated in plants to evaluate plant-nematode relationships and to establish nematode association, nematode involvement, or the role of the nematode in the disease development. Inoculation varies depending on the experimental purpose it will serve.

The first stage in studying plant-nematode relationships is a strong evidence of the suspected nematode involvement in the disease. Observing nematodes feeding or on in the host is useful at association stage and this can be done through general field observations, nematode surveys, soil fumigation studies and preliminary greenhouse inoculation experiments.

The second stage is to establish that the nematode is involved in the disease development. This is achieved by conducting inoculation experiments under controlled conditions. Observations and experiments may involve other microorganisms other than the nematodes which is the reason why graded series of nematode inocula may be added to the non-infested soil to establish a treated and non-treated check for comparison and correlation of the differences due to nematode population.

Experiments should be done under asceptic condition to establish the role of the nematodes in the disease or its activity in the plant. A microbiologically sterile single population of nematode should be used.

For the purpose of this experiment, Meloidogyne incognita, a root-knot nematode, is used to determine if it is responsible for the development of root-knots in Lycopersicum esculentum (tomato).

Methodology

A gram of infected roots were placed near the base of a set of tomato plants. Another set were prepared this time placing 20 grams of infested soil. The plants were arranged in the greenhouse following a randomized block manner. Initial plant heights were gathered and data were collected every week for four weeks. After four weeks, the final heights of the tomato plants were recorded. The tomato plants were removed from the pots carefully so as not to leave any plant roots on the soil. Afterwhich, the roots were washed to remove excess soil particles followed by the counting of the root-knot formations on the roots. The data were recorded.

Results and Discussion

The initial and final plant heights were recorded and the height differences were calculated.  Galls were also counted and were evaluated using the following index:  (RGI-Root Galling Index*) 1 – no gall, 2 – trace galling (1-25% galling), 3 – slight galling (26-50%), 4 – moderate galling (51-75%) and 5 – severe (76-100%).

Height differences were calculated so as to have a simple basis of comparison for the effects of the root-knot formation caused by Meloidogyne incognita on Lycopersicum esculemtum while the counting of the number of nematodes can be used for analyzing how the nematode population can affect the growth of the plant.

Below are the data gathered during the experiment:

Table 1. Data gathered for Lycopersicum esculentum with no inoculation to serve as control

Control
	Initial Plant Height (cm)	Final Plant Height (cm)	Height Difference (cm)	Number of Galls	Index*
Rep1	10.2	46	35.8	0	1
Rep2	13.5	59.6	46.1	0	1
Rep3	9	57.1	48.1	0	1
Rep4	11.5	53.4	41.9	0	1
Average	11.05	54.03	43	0	1

Table 2. Data gathered for Lycopersicum esculentum inoculated with Meloidogyne incognita using an infested soil as source of inoculum.

Infested Soil
	Initial Plant Height (cm)	Final Plant Height (cm)	Height Difference (cm)	Number of Galls	Index*
Rep1	10	46	36	149	5
Rep2	11	55	44	50	3
Rep3	11	52	41	31	3
Rep4	8.5	52	43.5	15	2
Average	10.13	51.25	41.13	61.25	3

Table 3. Data gathered for Lycopersicum esculentum inoculated with Meloidogyne incognita using galled roots as source of inoculum.

Galled Tomato Roots
	Initial Plant Height (cm)	Final Plant Height (cm)	Height Difference (cm)	Number of Galls	Index*
Rep1	10	41.5	31.5	102	5
Rep2	9	wilted	n/a	n/a	n/a
Rep3	10.5	61.2	50.7	284	5
Rep4	10	56	46	43	3
Average	9.88	52.9	42.7	143	4

Table 4. Average height differences, number of galls and index of the three treatments.

Source of Inoculum	Average Height Difference (cm)	Average Number of Galls	Average Index *
Control	43	0	1
Infested Soil	41.13	61.25	3
Galled Tomato Roots	42.7	143	4

Data has shown us that of number of galls is highest on plants whose source of inoculum was the galled tomato roots giving it a moderate galling (4) in the RGI while the control treatment showed no signs of galling, hence an index value of 1. The average growth of the plants has negligible differences so we look at the number of galls that were formed from t plants respectively and it can be noted that many galls were formed especially in the plants inoculated with nematodes from galled tomato roots. Hence, more nematodes came from the galled tomato roots. This means that between the two sources of inoculum, the use of galled tomato roots will yield more disease formation. It can also be noted that since the same galls from the inoculum were formed in the test plants, it can be concluded that the same nematodes were the cause of both the diseases observed.

Conclusion

Since the same gall formation were observed from the source of the inoculum and the test plants, it is confirmed that the presence of the nematode is indeed the cause of the disease since no galls were observed from the control set-up and galls were also observed from the roots of test plants inoculated with infested soil.

Tags: Nematodes, Plat Disease Diagnosis

In every field, weeds are always present. But what exactly are weeds? Well, some people define weeds as an unwanted, undesirable and useless plant. But no plant is completely useless. We may then define weeds as plants that are unwanted at a particular time and place and whose economic use has not yet been discovered. A plant species can only be called as weed if humans have not yet found a use for it. “One man’s crop maybe another’s weed.”

Some plant species though occur 99% as weeds in some fields. Echinochloa spp. and Monochoria vaginalis in rice fields for example. R. cochinchinensis and Cyperus rotundus in corn and vegetable fields respectively are considered as weeds. 10% of the 300,000 angiosperm species behave as weeds 99% of the time.

The unique characteristics of weeds have made them difficult to control in the field. They have excellent adaptations to disturbed environment and occupy the ecological spaces left open in agroecosystems. Other characteristics of weeds include their rapid vegetative growth, reproduce rapidly and mature early, very prolific and produce plenty of seeds, can survive and adapt to adverse conditions, dormancy of propagules or can be induced to dormancy under favorable environments, and are adapted to crop competition.

Rapid Vegetative Growth and Reproduce Rapidly and Mature Early

Weeds have numerous tillers for grasses, rapid tuber and shoot formation for sedges, and faster stem elongation and branching for broad leaves. Also, weeds are able to reproduce sexual and asexually. These have allowed the weeds to be able to maintain high population densities if not managed effectively. They also mature early so they are able to reach their reproductive period at a lesser time, hence more plants capable of to reproducing.

Very Prolific and Produce Plenty of Seeds

R. cochinchinensis can produce more than 700 tillers and branches and can produce inflorescence. Perennial weeds can reproduce rapidly through vegetative means through tubers, rhizomes, and stolon. Scirpus maritimus, a perennial sedge, can produce more than 100 dormant and non-dormant tubers in one cropping season in irrigated rice paddies.

Ability to Survive and Adapt to Adverse Conditions

Weeds are capable of resisting drought and excessive moisture stress. Large crabgrass (Digitaria sanguinalis) form contractile roots and arrests its growth during extremely dry conditions and resumes their normal conditions until a favorable condition is met. The common purslane (Portulaca oleracea) incline their leaflets upward to reduce exposure to sun during dry conditions thus reducing excessive moisture loss due to transpiration.

Propagules Possess Dormancy or Can be Induced to Dormancy

Dormancy is a mechanism that enables the species to survive under unfavorable conditions. This mechanism is common to weed species and until a favorable condition for growth is observed.

Adapted to Crop Competition

Weeds have proper synchronized germination. They are able to germinate at the right time in favorable environments. Their seedlings are fast growing and can be rapidly established. Their quick response to moisture and nutrient availability make them well adapted to crop competition in the agroecosystem.

It is very important to know the characteristics of weeds so that proper and effective weed management measures can be design to solve weed issues. What even makes it difficult is that weeds are also plants, like the crop planted in the field, anything that can harm them can possibly harm the crop as well. The soil too is a seed bank of thousands of weeds so it is expected that a weed can grow in empty spaces in the agroecosystem. Weeds are also are important in disease development because some weed species are alternate hosts of some pathogens. Weeds also provide a niche for other insect pests in the field, hence, controlling them is a very important management practice in the field.

Weeds are also plants. The crops planted in the field are also plants so how can we differentiate a weed from a crop?

Weeds are found on land where the native vegetation has been replaced by a controlled system of cropping management. It is man who has forcibly altered the vegetation for other purposes mainly for agriculture. Crops, on the other hand, are plant that fit economically into the scheme of man’s work and existence. These plants are being managed to a certain degree. A plant species become a crop because man developed it to be a crop.

In the early days, weeds were not considered as pests in the field since: a) damage caused by weeds are not visible as those caused by insects and plant pathogens, b) crops are always associated with weeds, c) it is easier to see insects with crops than weeds, d) and there is seldom total crop failure due to weeds.

Damage of weeds to crops is not visible compared to insects that result to feeding trails and to diseases causing lesions and necrosis. When there is a crop, there is always a weed. That is why weeds were not considered as a threat to crop production. Sometimes, weeds look like crops so it is difficult to spot weeds in a heavily planted field. Unlike pests which are very noticeable in the field. Crop failure is less likely attributed to weed competition and there is seldom crop failure. These are some of the reasons why weeds were not regarded as pests before. At present, the direct and indirect contributions of weeds in crop failure have made it one of the pests considered in the field.

Monocropping is said to be an unecological and unstable practice and is very prone to pest outbreak. Monocropping is a system that there is a single crop planted on the whole field for the purpose of more harvest and lesser work. This system is very popular in many parts of the world mainly for staple food crops and for export products as well as for the industry.

The problem of monocropping is that the field is more likely to experience high disease and pest incidence. This is due to the fact that in monocropping, there is a lot of supply of food favoring growth and reproduction of pests. Since pests are host specific, expect that pest population will increase at a high rate. In effect, the farmer needs to spray lots of pesticides on his field to prevent outbreaks. This practice is very unecological and unstable since pesticides can also kill the beneficial insects in the field.

Increasing diversity in farm therefore can help in decreasing pest population. Understanding some ideas on diversity can help us how to improve diversity in the farm.

Predators are polyphagous and have a very broad habitat requirements. Therefore, if there are more predators in the field, there are more natural agents that can control the pest population. A more diverse system can have more predators and therefore more pest control agents.

Monocropping provides abundant and concentrated resources as well as a homogeneous physical condition. As discussed earlier, monocropping can promote high levels of pest incidence and less predators. You can therefore use different varieties of the crop as this can increase diversity in farm. Since pests are host specific, it is recommended to plant local and adapted varieties of the crop together with hybrid varieties to ensure a stable harvest at the end of the season.

Spacing and Row Orientation can also contribute to diversity in farm. There are crops that are generally planted in 20×20 cm orientation for effective farm implement utilization and maintenance of the field. A more effective orientation of crop row and spacing is doing it in a 40×10 cm manner. This type of orientation results to more microenvironment in the field. It has less shading in the inter rows and is less humid. This results to lower pest population since predators are likely to occur in the field. Studies have also showed that an east-west direction of rows can increase yield by 10-12% and can decrease pest incidence better.

Planting trap crops not only increases diversity but it can also reduce pest attack significantly. Plant crops are planted to attract pests are they are more preferred by pests than the main crop. An example of a trap crop is corn to trap cottonball worms if your main crop is cotton and tomato to trap nematodes attacking pineapples.

Tags: diversity, monocropping, Pest Control, pest incidence

Rice bug is a significant insect pest in a rice field. It can reduce the total yield by 30% during harvest if not given attention by farmers. The insect feeds on rice at the milking stage (30-35 days after planting depending on the rice variety) of the plant leaving empty rice grains during harvest. Thus the reduce in the total yield.

A cheaper cultural method of controlling rice bug practiced by some farmers all over the Philippines is by dipping a cloth to a female urine and place it in sticks or poles placed in the boundaries of the field. The urine should come from a female who has already undergone menstruation or if she is already in her menstruation period. Farmers recommended using a wife’s urine as it is more effective than using an unmarried woman’s urine. Still, the latter’s urine can be used as long as she is already in puberty.

The reason for this is that male rice bugs are attracted to the female hormones secreted by the female rice bags. This hormone is similar to the human female hormone, thus, the male hormones will be attracted to the cloth (dipped in the female urine and stuck on a stick or pole) that you have placed in the boundaries of the field. By daytime, the male rice bugs will be gathered around these traps and you can manually kill the male rice bugs. Without the male rice bugs, there wont be any agents to fertilize the female rice bugs. Thus, the rice bug population will be reduced and that you don’t have to spend on additional costs for pesticide application. I hope this information helps.

Tags: rice, rice bug