The document discusses plant diseases and resistance. It notes that the relationship between a plant and pest is complex, depending on environmental conditions, the properties of the organism, and the plant's ability to defend itself. Varieties within a plant species can differ in their resistance. Pathogens are known to develop new biotypes or strains that can infect plants that were previously resistant. Resistance is defined as a plant's ability to restrict pathogen growth and damage compared to susceptible varieties in similar conditions with similar pathogen pressure. Resistant plants may still show some symptoms or damage under heavy pressure.

1. Production of Disease and
Stress Resistant Plants
III B.SC., BIOTECHNOLOGY
COURSE TEACHER
Dr. M. PAVUNRAJ

2. PLANT DISEASES AND RESISTANCE
The relationship between a plant and a pest1 is very complex.
The ability of a pest to cause disease in a plant depends on
environmental conditions, the properties of the organism itself and
the capacity of the plant to defend itself. Varieties within a plant
species can differ in their ability to defend themselves. Under
different climatic conditions the interaction between the same plant
and pest may have different outcomes.
Pathogens are known to develop and form new biotypes –
pathotypes, races or strains that can cause damage to plants, which
remain unaffected by the original form of the pathogen. Resistance is
the ability of a plant variety to restrict the growth and development of
a specified pathogen or the damage they cause when compared to
susceptible plant varieties under similar environmental conditions
and pathogen pressure. Resistant varieties may exhibit some disease
symptoms or damage under heavy pathogen pressure.

11. Rank Virus Author of virus description
1 Tobacco mosaic virus (TMV) Karen‐Beth G. Scholthof
2 Tomato spotted wilt virus (TSWV) Scott Adkins
3 Tomato yellow leaf curl virus (TYLCV) Henryk Czosnek
4 Cucumber mosaic virus (CMV) Peter Palukaitis
5 Potato virus Y (PVY) Emmanuel Jacquot
6 Cauliflower mosaic virus (CaMV) Thomas Hohn and Barbara Hohn
7 African cassava mosaic virus (ACMV) Keith Saunders
8 Plum pox virus (PPV) Thierry Candresse
9 Brome mosaic virus (BMV) Paul Ahlquist
10 Potato virus X (PVX) Cynthia Hemenway

12. Tobacco mosaic virus (TMV). (A) Systemic infection of Nicotiana tabacum cv. Turk plants
showing TMV‐associated mosaic. (B) Necrotic local lesions on N. tabacum cv. Glurk
leaf, demonstrating Holmes' N‐gene resistance following inoculation with TMV.