 Hi, welcome back. In the last class, so we learnt about the host plant resistance and the types of host plant resistance. Now, in this class, let us look at the mechanism by which the plants will develop these resistance mechanisms. So, there are three major mechanisms of resistance. One is the antigenosis and second one is an anti-biosis and third one is the tolerance. Let us look at in detail about what are these mechanisms, how they are going to impart the resistance in the plants. With this diagram, we can clearly look at the factors which are involved in developing or imparting the resistance in the plant. So, the antigenosis which is purely of the pest reaction in the sense. So, based on certain characters which are present in the plant, the pest is going to react to that and hence, so the plant will be get avoided by the pest attack. Whereas, in second mechanism that is an anti-biosis which is a purely a plant reaction. In the sense, the plant will produce in response to which the pest population is going to be reduced. Whereas, the tolerance mechanism is a reaction of both. It is both by the pest and as well as by the plant. Now, what is antigenosis? Basically, antigenosis can be simply defined as a non-acceptance. In the sense, it is a type of resistance where insect will not accept for feeding and breeding even if there is no alternative source. In the sense, the plant will have a certain mechanism or a characters which totally avoid the colonization of the insect on that plant and even if there is no alternative for it also, the insect cannot establish on it. For example, the host plant characters which are responsible as a non-preference for the insect for shelter, OE position and feeding. So, this mainly involves the presence of the morphological or the chemical factors which alter the behavior resulting in a poor establishment of the insect. If you look at these, some examples that I have given here. Say, for example, the trichomes in cotton that is means the long hairy character of the cotton on leaves and the stem are quite resistant to the white flag. Similarly, the wax coating on the cruciferous leaves like cabbage or cauliflower will deter the feeding by the diamond back mark and some of the ear-head characters or the plant shape or color will also play a major role in the non-preference of the insect. So, some characters like the open panicle in case of sorghum will not support the helicopa and also the ear-head bug. So, this table gives some of the characters in certain plants, I can add some of the insects. For example, for bowlworms, so you see the non-preference will be smooth leaves or nectarilus, long pedicel and thick bouldering. Whereas, for the bowl we will can see that frego bract kind of a plant, then red plant body, hairy leaves are the major non-preferring characters. For white flies, the smooth leaves and the thin leaves are the non-preferring character. Then coming to the next mechanism is an antibiosis. Antibiosis can be defined as an adverse effect of the plant on the biology with respect to the survival, development and reproduction of insect and their progeny due to certain biochemical and bio-physical factors present in it. So, it might be due to the presence or production of the toxic substances or absence of sufficient amount of the essential nutrients or causing an nutrient imbalance or the improper utilization of the nutrient. So, examples have been here like certain chemicals like dimbova, so which is mainly acts as an antibiosis against the European corn borer and the gospel content present in the cotton is an antibiotic factor against the American bullworm. Similarly, sinegrain is a compound present in the plant will deter or not establish make the plant, I mean the insect will establish on it for the aphids and cucurbitation against certain aphid species. Now, how these antibiotic factor or the antibiosis is going to affect the insect? So, if you look at there are two important way that it is going to affect one is the direct way and the indirect way. In case of direct way it directly affects the growth and development of the plant insect and also the development process and not only that it also affects the reproduction of the insect and ultimately affecting the survival and the general vigor of the insect. Indirectly it makes vulnerability to the biocontrol agent in the sense when the insect growth and development is affected then quite naturally the other natural enemies will take over and then so they will control the past. Then vulnerability to the environmental aberration its overall effect is the reduction in the rate of the population. Some of the biochemical components have been grouped here as an high gospel content for the bullworm or tobacco birdworm or even to the spider mite. Then high phenol content is quite confer the resistance to the bullworm and also the condensed a tannin so for the same past. In the high tannin content if it is present on the leaves then they are quite resistant against jacids. If they are present in the buds they are quite resistance against the bullworm attack and similarly the low sugar content in the anther is imparts the resistance to the bull we will and the bullworm. Now coming to the third mechanism of resistance that is tolerance. What is tolerance? The tolerance can be best defined as its ability of the plant to grow and reproduce and even repair the injury to a marked degree in spite of supporting a population approximately equal to that of a damaging as a susceptible host. That means the plant do not show any kind of an antigenosis or antibiosis but simply support the best population to a higher extent but still it will be capable of producing a normal yield. So there will not be any economic yield or a loss, there will not be a lowering of any quality of the product and in fact sometimes the tolerance will be confused with a lower level of resistance or the moderate resistance but it is not so and this is not it is totally different from that other two causes by not coming in or in other way of the activity which I have already explained. This is the table which indicates some of the there are crops which have been developed which shows the resistance against the various insect pests. So I will just make a passing remark like in case of ground nut on leaf miner so we have the ICGV varieties which have developed and imparting resistance against the leaf miner similarly in case of the chickpea against pod borer would we have some varieties which have been developed and for sugarcane for several pests on sugarcane we have these the co varieties which are quite specific in imparting the resistance against these plants. And what are the advantages of the host plant resistance? If you look at this basically the host plant resistance provides accumulative and persistent effect in the sense these characters are included or incorporated or integrated into the plant system so over a period of time and hence the characters are going to be established for a longer time. Then there is no additional cost to the grower in the sense like no extra pay should be made by the farmer as these are already been integrated or incorporated in the plant system and there are no residue effect and no effect or an harmful effect to the beneficial fauna and it integrates effectively with other control methods and also helps in conserving the biological control agents and it is most useful in the low economic crops but at the same time we also have certain limitations for the host plant resistance. What are those? There is a long time which is needed for developing and resistant variety and if you do it for a one pest so again it will be a longer rather than that better to develop a multiple resistant varieties and different varieties need to be developed for a different geographical areas and there is always a good agronomic practices to be made in order to conserve these characters against those insects and resistance most often is found in species of off type and biotypes especially which we see it in insects will adopt quite well and will break down the resistance in the plant and there is an incompatibility of resistance character with some other characters in the sense like sometimes certain plant varieties which show a lot of resistance to certain species will have a low yielding quality so this kind of an incompatibility we do see many a times and the replacement of varieties by the better yielders will be sometimes quite essential. Then how best that HPR or the host plant resistance can be incorporated into the IPM so this very well fits into the IPM practice say for example it can be very well fit into the chemical control where the HPR will enhances the efficacy of insecticide because it has already reduced the pest population make it more vulnerable even with a simple chemical spray. Similarly it is compatible with the biocontrol program like because the pest species will already is affected by the host plant resistance mechanism so thereby they will become more vulnerable to the various biocontrol agents and they are also quite fit well into the cultural methods as these cultural practices will help the better utilization of the resistant varieties. So in this class we actually learnt about the different mechanisms through which the plant will develop a resistance against the pest attack thank you.