I fully agree with Dr. Alex Ignatov in his perspective, as even in the field of animal diseases, the incidence and severity of infection depend on this triangle (host, pathogen, and environment) and every one of these parts affects depending on the factors that pertain to it, and in general, as the doctor indicated, we rarely find two severe pathogens for the same host at the same time, in the field of our specialty, we find more than one pathogen sometimes, but one of them is a predisposing factor for the other because the former works to weaken immunity, which prepares for infection with the other. And in our field of specialization, there is the primary pathogen, which has the ability to cause disease even when the immunity is normal, and the secondary pathogen that cannot compete with the primary but is waiting for the appropriate opportunity to occur for the disease. I'm sorry because I generally answered, that this is not my exact specialty, but I tried to give my view from a general perspective on infections and how pathogens compete for disease events. My sincere gratitude Doctor.

Arbind K. Choudhary The fact of synergism between plant pathogens in well known for many groups for microorganisms. It was more studied for viruses and bacteria, and less (as I know) for pathogens of different groups.

Look for some publications:

Lamichhane JR, Venturi V. Synergisms between microbial pathogens in plant disease complexes: a growing trend. Frontiers in plant science. 2015 May 27;6:385.

Vance VB, Berger PH, Carrington JC, Hunt AG, Shi XM. 5′ proximal potyviral sequences mediate potato virus X/potyviral synergistic disease in transgenic tobacco. Virology. 1995 Jan 10;206(1):583-90.

Le May C, Potage G, Andrivon D, Tivoli B, Outreman Y. Plant disease complex: antagonism and synergism between pathogens of the Ascochyta blight complex on pea. Journal of Phytopathology. 2009 Dec;157(11‐12):715-21.

Abdullah AS, Moffat CS, Lopez-Ruiz FJ, Gibberd MR, Hamblin J, Zerihun A. Host–multi-pathogen warfare: pathogen interactions in co-infected plants. Frontiers in plant science. 2017 Oct 25;8:1806.

@ Arbind K. Choudhary, In general after the attack of the one disease, the defense mechanism will be in place to fight with the infection. Since the defense mechanism is already in place for one disease, it may give chance to the second disease to attack the plant. It may also depends upon the interaction between the first and second pathogen attacking the plant.

I think that the plants listed are closely related (Family Leguminosae [Fabaceae]). Therefore, one pathogen can cause diverse infections on each of the plants with different severity levels. This observation is more of plant species relatedness ( collateral/alternate hosts) rather than pathogen synergism.

PS: To confirm my assertion, intercrop with Tomato, pepper, onion, ginger or garlic in the next planting season & see if the disease level reduces or not

Yes, because it may one of the pathogen can helps as antipathogenic effect over to the other pathogen.

Off course, the severity of one pathogen will affect the severity of another pathogen due competition between two for nourishment within the host. In case of Brassica, once white rust occurs, Alternaria blight will be less. Here we must consider the area affected by particular pathogen lowers the availability of surface for another pathogen. Therefore, the one pathogen will affect the severity of another pathogen.

Interaction between two pathogens can be more complex than just competition for free area on plant surface. Bacterium Pantoea ananatis, pathogen of many cereals and other plants can infect basidiomycete rust fungus, Puccinia graminis (and it is named as P. uredovora) Article Pantoea ananatis: An unconventional plant pathogen

@ P. D. Meena & @Alex Ignatov

I appreciate your contributions to the question asked.

If you study the question asked carefully, you will find out that the disease reported did not occur in the same season, therefore, there was little or no chances of the pathogens interacting or competing for food and space. Logically, a pathogen that is capable of feeding on different plants (Collateral or Alternate host plants) is natural programmed to have a favourite food source. It can feed & cause diseases in varying degrees on each of the plants in direct proportion to the way the food source inherent in the plant appear palatable to it.

Finally, when it feeds on its favourite plant species, the disease expression or severity is magnanimously devastating.

THIS IS PURELY A PROBLEM OF CHOICEST CARBON SOURCE FOR THE PATHOGEN TO DEGRADE & CAUSE DISEASE

@Peter Etaware

Actually the diseases reported occur in India during the same cropping season in cool season pulses such as chickpea and lentil.

Arbind K. Choudhary To be close to your question "Does the occurrence of one disease affect the intensity and severity of other diseases in plants?" I would remind that any disease incidence depends on 3 sides of the Triangle: host, pathogen, and environment. Very rare, two different pathogens of the same host have identical most favorable conditions for infection. Thus, it will be only one predominant pathogen at the same season. Of cause, real situation is more complicated, and two pathogens can attack plant parts in different microclimate niches or plant tissues of different age, etc. I have seen strict zonal occurrence of 4 related bacterial pathogens on different parts of plants in field.

Yes of course, occurrence of one disease affect the intensity and severity of other diseases in plants due to competition between two disease for shelter and to derive nutrient from host.

Dear @Rishav Pandit Thank you so much for your contribution. I appreciate it.

I fully agree with Dr. Alex Ignatov in his perspective, as even in the field of animal diseases, the incidence and severity of infection depend on this triangle (host, pathogen, and environment) and every one of these parts affects depending on the factors that pertain to it, and in general, as the doctor indicated, we rarely find two severe pathogens for the same host at the same time, in the field of our specialty, we find more than one pathogen sometimes, but one of them is a predisposing factor for the other because the former works to weaken immunity, which prepares for infection with the other. And in our field of specialization, there is the primary pathogen, which has the ability to cause disease even when the immunity is normal, and the secondary pathogen that cannot compete with the primary but is waiting for the appropriate opportunity to occur for the disease. I'm sorry because I generally answered, that this is not my exact specialty, but I tried to give my view from a general perspective on infections and how pathogens compete for disease events. My sincere gratitude Doctor.

Dear @Manal Hadi Kanaan Many thanks for your contribution and substantiating my empirical observation and the answer given by @Alex Ignatov, which according to you, holds true for animal diseases as well.

I would like to add, and in general, the severity of the disease is the result that occurs as a net of the course of the disease, which is a battle between the pathogen and the host, each of them trying to overcome the other, and certainly, the results of this battle will be affected by the surrounding environmental factors, so here we returned to the triangle he mentioned Dr. Alex Ignatov. But in general and most likely in order for the host to become infected with a specific disease, there are predisposing factors for the occurrence of the disease, and these factors may be general risk factors that weaken immunity or it may be another pathogen that weakens the host's immunity and predisposes him to infection with the other cause. This is my humble opinion and it is from a general perspective because it is not a specialist, but I would like to add that to clarify from the general point of view. Thank you very much, Doctor, sincere gratitude to everyone.

Dear @Manal Hadi Kanaan Thanking for sharing your observations. These are indeed valuable. I appreciate and value your observations!

There is a close relationship between the emergence of disease states and their severity and between the interaction and the effect that occurs between the host, whether it is an animal or plant, and between the environment surrounding it and the pathogen, as for the pathogen, this depends on the virulence factors that it has and its severity as these factors distinguish the pathogen. Patient to the last of them is primary, as it possesses virulence factors that enable it to cause disease even when the percentage of contamination is low and even when other causes compete with it, and also depends on the dose or to which the host is exposed, as each pathogen has a specific dose for disease events .... And there are factors related to the environment, such as inappropriate environmental factors, which are considered predisposing factors for the occurrence of diseases because they mainly weaken the host's immunity and are considered stress factors for the host ... And there are factors related to the host himself, which is the immunity of his body, whether this immunity is natural passes from one generation to the next or Acquired ... This scheme from my master's thesis illustrates this relationship on which the severity of the disease depends, as the result is either sporadic cases or they turn into epidemics that are difficult to control, and this was mainly the result of interaction between these factors and depending on the host immunity. Sorry for the long haul. My sincere gratitude to everyone.

Certainly, infecting a plant with a specific pathogen leads to a disturbance in the plant’s physiology and weakens its defenses against other pathogens.

It is a good question

Dear @Manal Hadi Kanaan Thank you for narrating the details of your observation. I appreciate your contribution and participation in the discussion.

Dear @Ahmed Saeed Mohmed @Bushra Mahmood Alwan I appreciate your individual contribution to the discussion. Thank you so much.

Yes may be as some diseases have synergistic effects with other diseases

Dear M.K. Tripathi Actually my observation related to almost negligible occurrence of wilt disease and severe infection of Stemphyllum blight in lentil during the preceding crop season. In pigeonpea, it is generally observed in north east plains that in the year when pod fly infestation is more severe, there is almost no appearance of pod borer and vice versa.

In human yes but in plants i donot think so

Dear Abdulhadi Mohamed Jumaa Thank you for your opinion. I do appreciate it.

Yes may be if it weakened the immune system