BSPP ‘Plant Doctor’ Quiz #3 – June 2021

The correct answer is:

Generalised stress.

Reddening (just as with yellowing) is often a sign of generalised stress. This may be due to a variety of factors, for example, abiotic pathogens and insect feeding.  Phosphate deficiency will often cause reddening of the lower leaves and can be diagnostic but that is not the only problem that induces this effect.

The incorrect answers were:

Definitely indicates a deficiency of phosphate

This is a common symptom of P deficiency but is not the only cause of reddening.

Insect larvae within the stem

The stress caused by insect feeding will often cause reddening of the upper leaves but many other problems will do this too.

Root problem of some sort

Root problems may cause stress, leading to reddening, but that is not always the case.

The correct answer is:

Bacteria

Bacteria can cause leaves to collapse due to rotting, but the tissue in this image does not appear to be rotten or water soaked. It appears to be healthy apart from the areas that have split open.

The incorrect answers were:

Physiological problem

This is what I think is causing the problem (although it is very strange as the plants either side are unaffected). Plants, usually fruits, can split open if they take up water too quickly. It may superficially look like insect damage or pathogen infection, but the wound is generally clean.

Phytoplasma infection

Phytoplasma infection can cause gross morphological changes to the development of a plant. There is no evidence that this symptom is due to a phytoplasma but this is the kind of symptom they can provoke.

Animal damage

It looks like a large animal has laid on the plant and snapped the leaf blade at the point of attachment to the petiole.  There is no sign of any infection at the site of breakage.

The correct answer is:

Healthy

Despite the obvious purple colour, these potatoes were totally healthy and tasted like the more familiar white potato.

The incorrect answers were:

Fungal infection

There are several fungal pathogens that will infect potato tubers but generally they will cause the tissue to soften and lose structure.  It you look past the colour you can see that the tuber is perfectly fine.

Nutrient deficiency

Phosphate deficiency will often cause the lower leaves to become reddened (as per question 1) but this does not extend to the tubers.

Water mould infection

The only water mould that will infect the tubers of potatoes is Phytophthora.  This is definitely not Phytophthora infection; the tissue would be wet and brown, not hard and purple.

The correct answer is:

They are on the side of the root and not in the middle

When considering if a lump is a gall or a nodule, one simple rule is: if you can detach it without breaking the root it is a nodule.  Nodules are always displaced to the side of the root, whereas galls usually appear to be part of the root.

The incorrect answers were:

They are not intensely coloured

Both galls and nodules are generally whitish. Galls may be creamy coloured and nodules may have a slight pink colour.

They are less than 4mm across

Nodules are always less than 4mm across, but galls can vary in size from a few millimetres to up to 15 mm and larger.

They are round in cross section.

Both galls and nodules are normally round in cross section.

The correct answer is:

The level of transmission into seed can be significant in some cases, but the proportion of infected seed varies by crop and virus.

A few viruses will be carried over into the seed of the plant in a few cases. The percentage of infected seed varies depending on the crop and virus.  (Pea seed-borne mosaic virus is a good example).

The incorrect answers were:

All viruses are passed on at a low rate in the seed, but the industry lives with this.

No. Some viruses may be passed on into seed, but this is relatively unusual.

Some viruses are always passed on through seed as it is the only means of spread

This is not the case and all viruses have some other means of infecting plants

The process of seed production will remove all viruses and what appears to be seed infection is actually contamination from seed coat.

Contamination of the seed coat does occur in some cases (e.g. TMV on tomatoes) but not many viruses can survive outside the host.  If the seed is contaminated, the virus particles can be literally washed off with bleach.

The correct answer is:

It is extremely important as it provides the sugars to fill the grain

In wheat, the flag leaf is the most important one to keep free of diseases. If only one fungicide spray is applied to a wheat crop, it is best to do it when the flag leaf has just emerged. This is not the case in other cereals where the flag leaf may play a relatively minor role (e.g. barley).

The incorrect answers were:

The flag leaf is unimportant as the ear has already formed by the time it emerges.

It is true that the ear has formed but there is no grain in the ear.

The flag leaf will shade the ear and actually reduces yield.

The ear itself does contribute to grain fill to an extent and there will be some shading, but that is insignificant and you want the flag leaf to be in full sun.

It is just as important as any other leaf.

With regard to grain fill, the importance of the leaves falls off rapidly as you descend the plant.

The correct answer is:

Only wheat

Urediniospores will always infect the host plant on which they were produced. It is the teliospores, which will give rise to the basidiospores, that will ultimately infect the barberry. From a crop protection point of view, a farmer needs to prevent the urediniospores re-infecting the wheat.

The incorrect answers were:

Wheat and barberry

See above

Only barberry

See above

Technically neither wheat nor barberry

See above

The correct answer is:

Zymoseptoria

Even if you are not familiar with wheat diseases, you should have been able to get to the correct answer by eliminating the others.  This is Zymoseptoria (previously Septoria). It is an extremely common pathogen on wheat, carried by rain splash. If it reaches the flag leaf, the yield will be considerably reduced.

The incorrect answers were:

Phytophthora

Phytophthoras are mostly pathogens of trees; potato, tomato, capsicum pepper and soybean are the only annual crops where it is usually a problem.

Yellow rust

Yellow rusts form long stripes of yellow pustules and cause little browning and cell death. (It is still extremely damaging.)

Natural senescence of the older leaves.

The lower leaves of wheat do senesce as the crop matures but do not do so in patches as seen here.

The correct answer is:

Well-developed head capsule and no prolegs (short stubby legs on the abdomen)

The larvae of beetles are grubs. They have a large head, no prolegs but often have well developed thoracic legs (true legs). However, in borers and stem dwellers, these may be extremely small.

The incorrect answers were:

Well-developed head capsule and multiple prolegs (short stubby legs on the abdomen)

This morphology is typical of a moth larva; a caterpillar.

No head capsule and multiple prolegs (short stubby legs on the abdomen)

This morphology is typical of a fly larva; a maggot (the prolegs may be very small)

No head capsule and no prolegs (short stubby legs on the abdomen)

This morphology is typical of a fly larva; a maggot.

The correct answer is:

Two chemicals with the same mode of action will not help to prevent resistance in the pathogen population.

It is always a good idea to blend fungicides to prevent resistance developing in the pathogen population, but if the two chemicals are from the same resistance group, resistance can still develop.

The incorrect answers were:

The chemicals are both systemic and it is preferable to have contact and systemic mix. 

It is common practice to blend a systemic chemical with a contact one. This is usually done to get the benefit of the systemic action with the economy of the contact.

The chemicals are considered to be old and newer ones are available.

The triazole group of fungicides have been available for several decades but they are still an important aspect of disease control.

The chemicals will counteract each other and effectively cancel each other out.

There is no suggestion that this is correct; both chemicals will stay active (until resistance develops).