From the magazine: No. 1 2014
Fania Zamalieva, Tatyana Zaitseva, Lyudmila Ryzhikh, Zifa Salikhova, Tatar Research Institute of Agriculture of the Russian Agricultural Academy
Fusarium wilt periodically affects potatoes in Tatarstan, but the epiphytotic spread of the disease in 2011 and its development in the subsequent years 2012-2013 made it possible to discover new features in its course, knowledge of which can be used to reduce crop losses. Diagnosis was carried out on the basis of a set of visual symptoms on potato plants, tubers, as well as based on the results of an analysis of latent infection of tissues from the vascular system of stems and tubers according to the method (Popkova K.V., Shmyglya V.A., 1980). The fungus we isolated from potato stems and tubers belongs to the genus Fusarium by spore type; identification to the species will be carried out in the near future. We can only note that when detecting a latent infection, we most often observed the formation of white mycelium, characteristic of Fusarium solana.
To separate dry rot, which occurs as a result of Fusarium wilt, from ordinary dry rot, which occurs when Fusarium is infected through a wound surface, this article introduces a clarifying name for tuber rot caused by Fusarium wilt - vascular fusarium of tubers.
Fusarium wilt of potatoes is a dangerous disease; it is harmful not only to the current year’s crop, but also to subsequent reproductions. Due to the transmission of infection with seed tubers affected by vascular fusarium in a latent form, it can cause thinning of seedlings and inhibition of plant growth in the next generation. The development of Fusarium wilt, if the pathogen has already penetrated the plant, largely depends on environmental conditions. Sources of fusarium are always present in the soil and only some weakening of the plants and favorable conditions for the development of the fungus (alternating wet and dry periods at high temperatures) are necessary so that the fungus can penetrate the plant. It is these conditions that we have increasingly seen in our republic in recent years.
The beginning of the epiphytoty of Fusarium wilt on potatoes was associated with the conditions of 2011: after the June heavy rains, as a result of which the soil completely lost its structure, and then, after a long period of drought, against the backdrop of high temperatures, very strong soil compaction and shrinkage occurred with the formation of cracks . The fungus began to penetrate the root system of weakened plants; this was also facilitated by ruptures and damage to the roots. The development of the fungus in the vascular system of the underground and then above-ground parts of the plants led to complete blockage of the conducting system and very early wilting of plants in July-August, with increased formation of tubers with stolon rot (Fig. 1, variety Nevsky). Heavy rainfall in June and the subsequent drought and high temperatures covered most of the territory of the republic, so Fusarium wilt in 2011 also affected all potato plantings - both in small-scale and large-scale production. The rains that fell in September softened the soil, but by this time the plants were already completely affected by the disease and withered.
rice 1. Nevsky variety tuber with stolon rot in 2011
Seed material used for planting in 2011, obtained locally a year earlier, was not infected with vascular fusarium, since in the anomalous year of 2010, tuberization took place in September-October at low temperatures and in humid conditions.
In 2011, the drying out of the soil in the second or third decade of July coincided with the period of tuberization in the mid-early variety Nevsky, and therefore this variety exhibited severe symptoms of the development of stolon rot on tubers.
Under the conditions of 2012, we observed two dry periods, which were accompanied by drying out of the soil and were dangerous for damage by Fusarium wilt - from the third ten days of June to the first ten days of July (20 days), and from the first to second ten days of August (20 days).
The seed material used for planting in 2012 was latently affected by vascular fusarium. In some farms, already during the storage period, the seeds of the early ripening potato variety Vitessa, which came from the southern regions of the Russian Federation, completely rotted. At the end of May - beginning of June, after repeated overhauls, the seeds of the mid-early potato variety Nevsky, grown on the farm of the Tukaevsky district of the Republic of Tatarstan, completely rotted. Some potato varieties did not show obvious damage by vascular fusarium when sorted, but after planting they showed severe thinning and weakened growth (mid-season variety Zekura on a farm in the Elabuga region).
In 2012, soil levels of Fusarium wilt infection were particularly high on farms that replanted potatoes in the same irrigated areas where potatoes were grown in 2011. It was in these fields that the most depressing picture was observed - germination was no higher than 50%, and the emerging plants were stunted in growth. There was practically no harvest or it was infected, among other things, with stolon rot and was severely rotten during storage.
Thus, the combination of soil contamination due to the lack of crop rotation and hidden contamination of seed material led to the worst results.
a) b)
Fig.2. Symptoms of fusarium wilt in the conducting system (a), in the vascular system of the tuber (b)
The condition of potatoes was significantly better in farms that grew potatoes under irrigation and in crop rotation. For example, the Arosa variety provided yields of 30-35 t/ha in farms in the Arsky and Tukaevsky districts; in addition, these potatoes were stored well, despite that in the field by September there was a massive prevalence of Fusarium wilt symptoms on the apical leaves of plants and browning of the roots (Fig. 3).
It should be noted that potato seeds of the varieties Arosa, Felox, Zekura, brought directly from Germany, not affected by vascular fusarium, when grown under irrigated conditions, in compliance with crop rotation, nevertheless, revealed a significant prevalence of symptoms of fusarium wilt, including on roots That is, favorable conditions - high temperature, humidity and drying out of the soil - were of decisive importance, the disease began to develop even in the absence of strong infection of the seed material and soil.
In 2012, the period of soil drying out in the third ten days of June and the first ten days of July coincided with the period of tuberization of early ripening varieties, therefore, agricultural farms observed an increased infection of tubers with vascular fusarium in the harvest of these varieties, in particular the Udacha variety (Fig. 2 b).
The prevalence of vascular fusarium in latent form was also highest in the early varieties Zhukovsky ranniy and Rozara, lower in the mid-early varieties Nevsky and Radonezhsky, and even lower in the mid-season variety Ladozhsky.
In small-scale production in 2012, seeds of low reproduction, latently affected by Fusarium, and contaminated soil led to low yields, even on relatively richer organic soils. Apparently, in suppressive soil, recovery from the infection accumulated in 2011 was slower than necessary due to lack of time to neutralize fungal activity.
Fig.3. Mass development of fusarium wilt in a potato field (epiphytoty)
Under the conditions of 2013, precipitation was even more uneven than in 2012. The emergence of seedlings and further growth of potatoes due to high temperature and drought in May-June occurred with a delay of about two weeks; during the growing season, the plants were weakened due to lack of moisture in the soil and high daytime temperatures. From the second ten days of July to the first ten days of October, five periods with two ten days repeated one after another - one with heavy precipitation and the other without precipitation. The first three periods took place at high daytime temperatures and contributed to the active spread of Fusarium wilt. The next two periods of heavy rainfall and lower temperatures caused fusarium vascular rot of tubers to transform into wet rot in the soil before harvesting began.
Potato planting material in 2013 was latently affected by vascular fusarium, but to varying degrees, depending on the variety and conditions of its cultivation on the farm in the previous year.
In the spring of 2013, we discovered another feature of the development of latent vascular fusarium on planting material of potato tubers. Under production conditions, the same material was germinated in the spring at different temperatures and different results were obtained. Potatoes that sprouted at a temperature of 15° C provided a yield of 20-25 t/ha, and tubers that sprouted at high daytime temperatures of 25-30° C rotted before planting. This observation made it possible to explain the case of 2006: then we sent part of the seed potatoes to Astrakhan for summer planting, but the material completely became unusable in just a few days. At the same time, potatoes from the same batch in the fields of our republic provided a good harvest.
Apparently, at high temperatures, which have been observed in the republic in recent years during spring germination, we create conditions as favorable for the development of vascular fusarium in tubers as in Astrakhan during summer planting.
Thus, high temperatures (above 20-25 C) during spring germination stimulate the development of the fungus in tubers latently affected by vascular fusarium.
Under conditions of regularly repeated drying out of the soil in 2013, all potato varieties, to one degree or another, were affected by Fusarium wilt in the field, and tubers were affected by vascular fusarium (Fig. 4).
Due to the increased air humidity and low temperatures during harvesting, the potatoes entering the storage facility were poorly dried, so already in the fall, increased rotting of the tubers was observed in the warehouses, the cause of which was vascular fusarium, which affected the tubers in the field. The prevalence of vascular fusarium in latent form on seed potatoes of some varieties grown locally averaged 2014-15% in February 20.
a) b)
Rice. 4 Symptoms of fusarium wilt on potato plants in 2013:
a) anthocyanin coloring and folding of the apical leaves into a boat,
b) dry rot (rottenness) of the underground part of the stem.
Summary
After the epiphytotic infection of potatoes by Fusarium wilt in 2011, the spread of the disease in the republic has been continuing with greater or lesser success for three years. It must be borne in mind that in this case two multidirectional processes continue simultaneously. The first is the recovery of soil and potatoes from disease. The second process is a new infection caused by annually recurring conditions favorable for the development of the fungus.
According to our observations, after 100% infection with fusarium wilt of potatoes in 2011, there is a gradual recovery of soil and seed material from vascular fusarium.
As the experience of 2012 showed, the greatest danger is the soil on which the growth and death of plants affected by Fusarium wilt took place. Therefore, potatoes must be grown in crop rotation. In suppressive soil, the sources of Fusarium wilt are suppressed, but after severe epiphytoties, such as in 2011, the activity of soil microflora may not be enough to suppress Fusarium the next year; additional measures are necessary.
Fungi of the genus Fusarium are facultative parasites or saprophytes. They actively decompose dead plant debris that falls into the soil, and thus perform a useful function. But when stressful conditions occur, weakened (half-living) plants can be affected.
On personal plots, the autumn application of organic fertilizers can help to intensify the saprophytic activity of the fungus in decomposing organic residues, and the spring application, especially in a dry spring, can, on the contrary, contribute to the drying out of the soil and increased parasitic activity of the fungus.
Good, regular watering can lead to healthier soil and crops. Irregular watering, which causes the soil to dry out after heavy irrigation, can increase Fusarium wilt disease. With high soil moisture, Fusarium develops well, and with subsequent drying out, it attacks weakened plants, since most of the fungal antagonists apparently die in dry conditions.
Seed material latently affected by vascular fusarium can produce an unaffected crop, that is, the transmission of fusarium to offspring is not one hundred percent and depends on the prevailing external conditions. Providing plants in the field with fertilizers and moisture allows them to resist disease.
The quality of the seed material is very important: high reproductions, free from viral diseases, grow actively and are more resistant to damage by Fusarium wilt.
It is necessary to control the development of fusarium when storing tubers. Excessively high temperatures when germinating tubers in the spring can lead to increased development of the fungus, which can lead to complete rotting of the potatoes.
It is possible to predict the development of vascular fusarium depending on the potato variety - if the period of its tuberization occurs in conditions of high temperature and drying out of the moist soil, then the hidden infection with vascular fusarium will be more widespread.
When storing tubers with hidden damage by vascular fusarium, the initial stages are especially important - drying, curing period, cooling. It is necessary to dry the surface moisture on the tubers as quickly as possible, since with its help the infection multiplies, and then pockets of wet rot appear. If tubers arrive in storage wet (as in 2013), it is necessary to dry them around the clock until moisture is completely removed from the surface of the tubers.
To radically change the situation with root rot and combat Fusarium wilt damage when the soil dries out, it is necessary to increase soil fertility, introduce green manure crops into crop rotations, and create a mulch layer that reduces moisture changes in the soil.
Seed grown in southern regions may have a higher latent infection with vascular fusarium due to the high temperatures inherent in these zones.
Forecast for 2014 year
In 2014 year Potato planting material will be less affected by vascular fusarium due to the visual manifestation of the disease and the culling of affected tubers already in the fall during harvesting. Further development of the disease on plants in the field will depend on germination conditions and weather conditions during the growing season. In order for plants to resist disease, it is necessary to create optimal conditions for them.
Additional recommendations for protecting potatoes from Fusarium wilt:
- use high reproductions for planting (super elite, elite, first reproduction), which have high growth energy and are able to resist diseases;
– grow varieties with different ripening periods to reduce the risk of the tuberization period coinciding with moments favorable for the development of Fusarium wilt;
– tubers should be germinated after sorting at a temperature no higher than 8-15° C, avoiding the formation of long sprouts;
– do not deepen – the maximum planting depth should not exceed the diameter of the tubers – 5-6 cm;
– observe the temperature regime when planting – the optimal soil temperature at the planting depth is 8° C (second ten days of May). In case of moist soil and sudden air warming to 25-30° C, we recommend delaying planting for one or two days to concentrate the activity of the fungus on saprotrophic activity for processing organic residues in the soil;
– grow potatoes on large-scale farms in 4-5 field crop rotations, and on personal plots – with alternation of crops and the application of organic fertilizers;
– monitor the condition of the top layer of soil – the soil should be loose at a depth of 20 cm;
– carry out pre-planting treatment of tubers (it increases germination and accelerates plant growth, therefore, protects against disease):
- microbiological preparations – “Fitosporin MF”, “Flavobacterin” + “Agrofil”, “Extrasol”;
- biologically active drugs - “Zircon”, “Siliplant”, “Epin-Extra”, “Melafen”, “Albit”, humates, etc.;
– apply basic fertilizers in calculated quantities for the planned yield, depending on the availability of irrigation, soil availability, and method of application;
– during the period of budding and tuberization in production conditions, carry out double foliar feeding with “Aquarin” (They showed high efficiency, and, what is especially important when stressful drought conditions set in, the effect was observed within a few hours, so “Aquarin” can be called an “ambulance” ); under conditions of normal humidity and irrigation, the effectiveness of all other biologically active drugs is high;
– do not allow the soil to dry out when irrigating potatoes;
– mow the tops 7-10 days before harvesting to cork the tuber skins;
– pay special attention to drying tubers when storing them in years with wet conditions;
– avoid sweating and waterlogging of tubers during storage.