BSPP ‘Plant Doctor’ Quiz #7 – October 2021

The correct answer is:

Genetic disturbance.

The yellow regions are distributed as zones. This strongly indicates a genetic issue within the leaf.

The incorrect answers were:

Lack of nutrient: symptoms of nutrient deficiency can affect regions of the leaf (veins, edges etc) but would not show up in zones of the leaf such as this.

Viral infection: the blocks of yellow are not typical of viral infection, it is often more of a pattern of yellow and green across the entire leaf; a mosaic.

Herbicide spray damage: yellowing is a common symptom of herbicide damage but the clear lines of yellow and green could not be due to the effects of herbicide.

The correct answer is:

Remove all weeds as they will impact on yield.

It is extremely unlikely (but not unknown) that a pathogen would reduce the impact of a weed population in an agricultural setting. You are better off to remove all weeds. NB. Pathogens are used very successfully in classical biological control.

The incorrect answers were:

Leave the infected weeds so that the disease could spread:  the disease may spread from the infected weeds to uninfected weeds but the competition from the original weeds would be too great to justify this plan.

The removal of the weed depends on the potential for the disease to spread to the crop: some diseases can spread from weeds to crops but see the answer above.

Leave all the weeds so that the disease can spread to healthy weeds: it would be foolhardy to leave all the weeds thinking that the pathogen would take care of them.

The correct answer is:

Mycotoxin production by the fungus causing the wheat to be unsafe to eat:

Infection of the ear will lead to mycotoxin production in the grain. These mycotoxins are usually present at extremely low levels but are extremely toxic.  They cause cancer at low concentrations and rapid death at higher concentrations. Wheat rarely has sufficient concentrations to cause immediate death but that is not the case with poorly stored maize.

The incorrect answers were:

Yield reduction due to the infection of the ear: this will have an effect but is relatively small compared to the effect of toxin accumulation.

Allows other more damaging pathogens to enter the ear: there is no evidence that this is the case.

Will return to the soil where it will cause root disease next year: Fusaria are fungi that survive well in the soil but that is not the primary problem with ear infection of wheat.

The correct answer is:

Viral infection:

The distorted growth is typical of a viral infection.

The incorrect answers were:

Bacterial infection: distorted growth is not associated with bacterial infection.

Downy mildew infection: systemic infection by a downy mildew is rare but when it occurs it can distort the leaves, this is not systemic infection by a downy mildew.

Nematode infection: wilt and yellowing are the symptoms commonly associated with nematode infection not leaf distortion.

The correct answer is:

All four:

The symptoms of sun scorch are seen in this photo.  There is always a severe transition between the healthy and dead tissue.  Other abiotic factors can do this such as fertilizer scorch and damage from some herbicides.

The correct answer is:

I don’t know and I don’t want to guess:

I appreciate that this is a bit of a cop out from me, but if anyone has any suggestion as to the cause of this extremely unusual symptom I would be glad to hear it.

The other answers were:

High temperature and dry weather: not symptoms associated with these conditions.

Mineral deficiency: there is no mineral deficiency that gives these symptoms.

Viral infection: possible as viruses can create very unusual symptoms but it is far from typical in every regard.

Herbicide damage: possible but the other leaves on the plant were unaffected.

The correct answer is:

Unrelated; two different rust fungi:

The photo on the left is brown rust and that on the right yellow rust.

The incorrect answers were:

They are the same fungus and the environment has caused the difference in colour: the environment does not cause a great deal of colour change in rust spores.

They are the same fungus but producing different spore types: rust fungi do produced different kind of spore within the same pustule but these are almost always black.

The same fungus but darker spores are older: rust spores don’t darken with age. 

The correct answer is:

Phosphate:

Stunted growth and reddening of the leaves (especially the lower leaves) is a classic sign of phosphate deficiency.

The incorrect answers were:

Nitrogen: yellowing of the lower leaves is typical of nitrogen deficiency.

Potassium: leaf edge scorch of the lower leaves is typical of potassium (K) deficiency.

Molybdenum: deficiency in molybdenum is not often seen except in brassicas. The symptoms are reduced laminar and cupping of the laminar in the upper leaves.

The correct answer is:

High humidity:

The conditions for the sporulation (production of downy growth) are high humidity and darkness. The darkness is pretty well guaranteed at night unless the leaves are in experimental conditions. High humidity often occurs when there has been rainfall and then the temperature drops. To test for a downy mildew, put a symptomatic leaf in a plastic bag overnight in the dark and look for sporulation in the morning.

The incorrect answers were:

High temperature, high light: the downy mildews do not thrive in such conditions and the infected areas often turn necrotic and die.

Low temperature; low light: under these conditions it is likely that sporulation will occur due to the concurrent increase in relative humidity but it is the humidity that is the important factor.

When free water has splashed up onto the underside of the leaf: the downy mildews will not sporulate into free water, the leaf must be dry.

The correct answer is:

Insecticides are generally more toxic than fungicides:

Fungicides are toxic but their toxicity is generally much less than that of the insecticides.

The incorrect answers were:

Fungicides are generally more toxic than insecticides: the reverse is true.

The toxicity of both fungicides and insecticides is about the same: this is not the case.

It is the formulation of the active ingredient that affects its toxicity and not the product itself: the formulation of product does not affect the toxicity of the active ingredient but it may affect your exposure to the chemical.