There are many causes of disease and death in plants. Which of the following is due to a pathogen? Soil mineral deficiency leading to limited growth, cattle grazing for dairy farming, herbicide spraying to control weeds, heavy metal contamination from factory effluent, or potato blight leading to a reduction in crop yield.
Let’s have a look at some of the key terms in the question before we tackle answering it. Pathogens are biological agents, such as bacteria, viruses, fungi, or protists, that can cause disease. Disease often leads to plant death, and these pathogenic infections are risky for plant populations as they spread rapidly between individual organisms.
Let’s have a look at an example of infectious disease in plants and the pathogen that transmits it. In this image, you can see some healthy potato plants. Potato blight is a disease caused by the spores of a fungus-like protist that has infected some of these potato plants, causing them to rot and decay. The spores of this pathogen spread easily in the wind so they can transmit the disease between individual potato plants, especially in wet and windy conditions. This means that it can infect mass numbers of plants quickly, leading to a significant drop in plant survival and therefore crop yield.
Let’s have a look at the answer options to see which is caused by a pathogen. Plants need to absorb mineral ions from soil. For example, nitrates help plants to make proteins for growth. A deficiency in mineral ions can lead to plant death. But this is not caused by a pathogen, so it cannot be our correct answer. Herbivory, for example, through cattle grazing, can also lead to plant death. Many humans encourage herbivory by demanding the breeding of more and more animals to eat for the meat industry and for the products they produce, such as milk for the dairy industry.
Herbivory is not an example of a pathogen causing disease and therefore plant death, however. So this option is also incorrect. Herbicides are often used by farmers to kill weeds and unwanted plant species. So there is less competition with the crop plant. Herbicides can spread, however, and contaminate other sources to kill plant species which were not the target. Herbicides are not an example of a pathogen causing plant death, however, so this option is incorrect.
Heavy metal contamination and other environmental pollutants from factory effluent can also cause plant death. When these heavy metals leach into water sources, they can easily enter soil and be taken up by plants, which kills them when they’re in high concentrations. Contaminants from factory effluents are chemicals and not biological agents like pathogens, however, so we can rule out this option too. Therefore, the option correctly describing disease-causing pathogens leading to plant death is potato blight, leading to a reduction in crop yield.