**5.1 Diseases transmission via vector**

Plant diseases can be caused by various factors. Such factors could be abiotic such as nutrient deficiencies, soil compaction, salt injury or sun scorch. Biotic causes of plant disease transmission are caused by living organisms and they are collectively named as pathogens. Understanding pathogens life cycle, living requirements, movements and disease they carry can allow effective implementation of management regime to intervene the cyclative transmission.


*a NPV, nonpersistent stylet borne viruses.*

*b SPV, semipersistent foregut-borne viruses.*

*c PCV, persistent circulative (mostly nonpropagative) viruses.*

*d PPV, persistent propagative viruses.*

*e Includes 110 virus species of the genus Potyvirus, family Potyviridae.*

*f Virus species of the genus Begomovirus, family Geminiviridae.*

#### **Table 2.**

*The table illustrates the major group of insect that cause the virus spread through vector. The viruses have also been categorised to persistency in the environment [11].*

#### *5.1.1 Insects*

Diseases in plants can also be transmitted via vectors. Aphids (28%) and whiteflies (18%) have been studied extensively over the years as they have been identified as common pathogenic vectors alongside with beetles (7%) and nematode (7%). However, the dense forests and every different area of land would always lead to a new discovery of a new species. In recent years, there is a new species of wasp, *Allorhogas gallifolia*. This wasp would make use of other wasp's gall as nests. Larvae that hatch would then feed on caterpillars that consume gall tissues. A caddisfly, *Potamophylax coronavirus*, has also been discovered. This moth has eggs and larvae that thrive in the environment near rivers and lakes. With new insects emerging, there are various study opportunities apart from just their life cycle. They can potentially be a reservoir host for all kinds of diseases to humans, animals and plants. The type of insects would often carry similar viroid.

Insects as vectors are relatively tricky to have a proper management to fully eradicate the population. This small, hardy population has found itself thriving through different ages of the earth by having the capability to populate through laying multiple eggs. These eggs laid by one are then sufficient to replace more than one adult in the population. With the rapid replication ability, insects are able to adapt to the changing environment through different mechanisms. Insects can transmit in a cyclative manner where the pathogen is ingested before passing on to the new plant host. Calculative plant pathogens will often induce physiological changes in their plant hosts. Vectors who then feed on the infected plant will then have behavioural changes to optimise the spread of pathogens to other plants. Their ability to invade a new area is dependent on the insects' ability to adapt to the environment besides the food availability.

#### *5.1.2 Herbivore as vector*

Herbivores are essential to the plant communities as grazing removes substantial quantities of biomass and promote plant species diversity [16]. In addition to herbivore vertebrate, insects have been shown to promote species richness by feeding competitive dominants. An instance to display such phenomena would be molluscs. They are a major group of invertebrate in temperate grasslands. These principal forb feeders would contribute negative impacts on species richness. These invertebrates are more well studied compared to soil-borne fungus. The complexity of the pathogen physiology is hard to comprehend as the environment will cause compensatory and additive interactions. Apart from infecting plants. Pathogens have displayed that they have the ability to increase plant susceptibility to herbivores to feed on the plant. Pathogens could also decrease it's susceptibility as it makes the plant less palatable to grazing animals.

#### **5.2 Soil-borne pathogens**

Besides insects as vectors for pathogens, they could be soil-borne as well. They are capable of spreading via swimming spores of primitive and soil-inhibiting pathogenic fungi. Fungal pathogens have been categorised into three functional groups: biological controllers, ecosystem regulators and species participating in organic matter decomposition and compound transformations. Fungal pathogens are dispersed by spores. Their successful inhabitants of soil is accredited to its high plasticity and their ability to adopt various forms in response to adverse or unfavourable conditions [5]. Biological controllers can improve soil health by regulating *Earth's Energy Budget Impact on Grassland Diseases DOI: http://dx.doi.org/10.5772/intechopen.99971*

diseases, pests, and the growth of other organisms. Fungi as ecosystem regulators are responsible for soil structure formation and medication. This will enhance the habitat of other organisms through the regulation of the dynamic aspect of the physiological processes in the soil environment.

Infected grasslands were observed to have increased species richness. However, This would have a negative impact on the dominant species in the grassland. In addition, the affected grassland will have decreased biomass. In a study by Allan et al. (2010), the biomass of the grassland will increase in an increasing exponential manner over the years. Fungal pathogens are not harmful to all. Despite the harm the bring to some of the species, fungi actively participate in nitrogen fixation, biological control of root pathogens, production of hormone and protection against drought. For instance, fungi can be beneficial to some leguminous crop via the improvement of plant uptake of nutrients and provide some form of protection to pathogens.

Nevertheless, bacteria that cause diseases in plants. Bacteria could be transmitted via the similar route as viruses by having physical contact on the health leaves or introducing plant materials that have bacteria. The simple transmission mode carries a huge load of impact on the environment as it alters the plants' physiology.
