When to prune strawberry plant roots

Strawberry cultivation is one of the main activities explored on small properties in Rio Grande do Sul (RS), especially in the South region, Vale do Caí and Serra Gaúcha. Bare root seedlings are used in the establishment of fields cultivated in the annual strawberry production system in this same state. One of the practices that ensure successful establishment of strawberry seedlings is planting at an adequate depth. This is an important precaution, as it must ensure that the root system is completely covered and that the base of the crown, where new leaves and inflorescences are emitted, is not covered by the soil.

National production of strawberry seedlings is not sufficient in quantity or quality to meet the demand of the main producing regions in Brazil. In Rio Grande do Sul, most producers use seedlings imported from Chile and Argentina. These two countries have characteristics suitable for seedling production, such as high latitudes, low precipitation, mild summers with a significant reduction in night temperatures, sandy soils and abundant solar radiation, in addition to being permitted the practice of soil fumigation with chemical products, eliminating possible sources of pathogens. Such characteristics favor the accumulation of reserve carbohydrates in the crown and roots, providing the production of vigorous seedlings, which will guarantee rapid post-transplant establishment and growth in the crop, providing high productive potential, also guaranteeing the sanitary quality of these seedlings.

Generally, imported seedlings have a long root system, measuring between 20 and 30 centimeters in length, a high volume of roots and are transplanted into beds covered with mulching. At the time of planting, the volume of roots can exceed the size of the hole, causing the roots to curl, which can lead to a reduction in the absorption of water and nutrients, causing unwanted stress and even the death of the seedling.

For this reason, some producers have used the technique of pruning part of the root system, in order to facilitate planting and minimize the frequently observed unwanted effects. However, with pruning, parts of the seedling's reserves, which would be used for plant growth and issuing new leaves, are lost.

In 2010, Embrapa Clima Temperado (CPACT) developed a study in which the effects of pruning the root system of strawberry seedlings during pre-planting were evaluated, on seedling survival and productive performance throughout the cycle. Bare-rooted seedlings from the Patagonia region in Argentina were used in the experiment, with an average crown diameter of 12mm and a root system with an average length of 25cm.

Three cultivars (Camarosa, Florida Festival and Camino Real) and three pruning intensities were evaluated: pruning of 1/3 of the length, pruning of 2/3 and no pruning of the root system, being carried out at the time of planting, using sterilized scissors. The cultivation system adopted was low tunnels with drip irrigation and fertigation.

In this trial, irrigation was maintained above field capacity for the first few weeks. The survival rate of seedlings after planting was not influenced by different cultivars and pruning intensity. Overall, the seedling survival rate was 98,9%.

In the strawberry production and marketing system in the southern region, the precocity of fruit production is an important characteristic, since the best prices for the producer are obtained from May to July. The shorter the time interval from planting seedlings to the beginning of harvest, the earlier a cultivar is. This characteristic is intrinsic to each cultivar, some are early and others are late, but it is also affected by the quality of the seedling and climatic conditions after planting. In the study carried out by Embrapa Clima Temperado, pruning the root system or the lack thereof did not affect this variable, demonstrating that vigorous seedlings have a high capacity for regeneration of the root system, to the point of not harming the development of the aerial part.

The pruning variation of the root system did not influence the variables related to growth, development, production and fruit size of the three cultivars studied. If root pruning is not carried out, the twisting of the root system during planting can cause a limitation in the nutrient absorption capacity, since the deformations caused in it offer resistance to the flow of water and nutrients. Furthermore, there may be an imbalance in growth regulators, which could compromise growth and production.

The results of this study agree with those obtained by North American researchers, who also found no differences in the survival rate, growth, production and incidence of diseases in plants that had their root system pruned before planting in the production field. These results suggest that the strawberry root system has a considerable capacity for regeneration due to the constant renewal of its roots throughout the crop cycle.

The strawberry root system is made up of two types of roots: adventitious and fasciculated. Adventitious roots, also known as primary roots, are those that develop from the crown and their main function is to reserve carbohydrates. The fasciculated or secondary roots, on the other hand, originate from adventitious roots, being responsible for the absorption of water and nutrients. The rapid development of fasciculated roots after transplantation is vital for the survival, growth and development of the aerial part of the plant.

It is possible that this particular effect of rapid regeneration occurs due to the high vigor of the seedlings produced in the Patagonia region of Argentina. Possibly, the rapid renewal of roots is associated with the high availability of reserves in the crown. It is believed that the reserves remaining in the roots after pruning would be sufficient to meet the needs during the regeneration phase and emission of new roots. Seedlings that have an aged, poorly developed root system, or with a crown diameter smaller than 8mm, should not undergo pruning of the root system, due to the reduced accumulation of reserves, minimizing their capacity for regeneration and recovery after planting. Furthermore, they are more susceptible to attack by soil-borne pathogens, leading to higher seedling mortality rates.

The results of this work allow some inferences about the practices carried out in commercial strawberry cultivation. No losses were observed in early and total fruit production when the root system of the seedlings was pruned before planting. This means that pruning the root system of seedlings can be a technique to be used to assist the producer when planting in the field, in order to minimize the incidence of poorly planted seedlings. However, cutting the root system can be an entry point for soil-borne fungi, which infect the roots and have the capacity to cause the plant to collapse and die. In view of this, it is recommended that, when pruning the roots, the seedlings are dipped in a fungicide solution, to prevent fungal attack. Furthermore, in areas with a history of soil fungal infestation, root pruning is not recommended, as it may compromise plant survival, leading to a high mortality rate.

 Click here to read the article in Cultivar Vegetables and Fruits edition 80.