**3.3 Production of quality seed plants/tubers**

The production of potato plants requires considerable agricultural practices. This involves the vegetative production of tubers which do not deviate in any way from the original characteristics of the variety and which free diseases.

Although "True potato seed" regeneration was initially the only means available to producers a clonal breeding model was then developed at the beginning of the 20th century in order to preserve the intrinsic qualities of the cultivars produced [11–13].

*Production of Potato Quality Seeds in Mountainous Region of Central Africa DOI: http://dx.doi.org/10.5772/intechopen.107126*


#### **Figure 3.**

*Agricultural calendar for very early varieties (CIP 720118, CIP 381381.20 and Rw 8201-19).*


#### **Figure 4.**

*Agricultural calendar for Early potato Seed Varieties (CIP 386003-2, CIP 393077-54, CIP 393371-50).*


#### **Figure 5.**

*Agricultural calendar for Late potato Seed Varieties (CIP 800949, CIP 381391-13, CIP 381395-1, CIP 383120.14, CIP 387233.24).*

The development in the recent past of in vitro potato micropropagation techniques combined with new quality control techniques (ELISA, PCR, etc.) has led to a significant increase in the overall quality of production. Micropropagation has also provided more flexibility and speed in plant production processes. These two methods will be developed below.

#### *3.3.1 Traditional Inbreeding and clonal selection*

This method includes the application of techniques that maintain the preservation of good health over time, namely [4, 6, 13]:

1.Selection of mother tubers on apparently healthy plants,

2.Tuber growth in areas of unfavourable climate for viral infections;

3. Isolation of propagating crops from infected consumer crops;

4. Severe mass selection in propagating crops;

5.Early dehaulming to remove leaves from plants and prevent them from infections.

#### *3.3.1.1 Selection of mother tubers on apparently healthy plants*

It is essential, before multiplying a potato clone, to ensure that the seed tuber is free from any disease, including virus-borne diseases.

The tuber is chosen from the healthy batch (varietal collection, family field, etc.) and then undergoes a series of various tests (ELISA, visual checks, etc.) to verify the absence of any infection.

Sometimes there may be no healthy tubers (old varieties chronically infected with one or more viruses). Since viruses are mostly absent from seeds and meristem, regeneration from meristem and thermotherapy can help to cure these diseases and thus obtain a healthy starting material.

These very fine techniques have proven their effectiveness for a long time.

Meristem culture consists of growing in vitro a very small fragment of the apical shoot which is generally virus-free. This technique gives very good results, provided that only the strict meristematic zone is sampled (of the order of 0.3 to 0.5 mm).

#### *3.3.1.2 Tuber multiplication in unfavourable climates for viral infections*

Except for the generation F0 production or subsequent in vitro propagation and micro-cuttings, the majority of subsequent multiplication is done in the field and the impact of the environment is then essential to producing good quality plants. Indeed, zones with a climate unfavourable to the propagation and dissemination of aphids (cool and humid regions, with frequent winds) make it easier to maintain a good sanitary condition of the crops. Following methods can be applicable:

#### *3.3.1.2.1 Removing diseased plants*

In addition to these environmental precautions, it is also necessary to eliminate the sources of inoculum that are infected virus plants themselves inside the crops.

*Production of Potato Quality Seeds in Mountainous Region of Central Africa DOI: http://dx.doi.org/10.5772/intechopen.107126*

This cannot be done before planting, as the tubers infected by virus generally do not show symptoms, with the exception sometimes of some discolouration on the sprout.

On the other hand, the foliage of contaminated plants expresses various specific symptoms of the virus notably, leaf roll, mosaics, curly, stunted, etc. These symptoms may be more or less easy to observe depending on the varieties, vegetative stage and climatic conditions and laboratory techniques may be required in addition to visual examination. The knowledge of these visual symptoms helps to eliminate diseased plants (purification) in a continuous way during the period of growth of the foliage.

#### *3.3.1.2.2 Removal of regrowth and other sources of viruses*

Another source of contamination is regrowth, plants from small-scale tubers left on the ground after harvest. The number of these tubers can exceed one hundred thousand per hectare, there is no effective means against this regrowth except the respect of a certain rotation time.

#### *3.3.1.2.3 Limiting passages*

In order to limit the spread of contact-transmissible viruses (PVX and PVS), it may be useful to limit the passage of tools, machines and humans.

The cultivation operations will also be done always starting with the healthiest plots, to avoid contaminating them hard to pass into the affected plots.

#### *3.3.1.2.4 Protective treatments*

Control of vector aphids is first carried out by chemical means. It is especially effective in preventing the spread of so-called persistent viruses (PLRV) whose particles are infectious only after a certain period of residence inside aphids. So, we can destroy the aphids first. The spread of non-persistent viruses, among which PVY is particularly important, is much better contained by the application of mineral oils. These nevertheless have some disadvantages: by maintaining moisture on the foliage, they may promote the development of Late Blight and make it more difficult to purify certain varieties whose leaves may deform as a result of phytotoxicity.

#### *3.3.1.3 Isolation of propagating crops from infected consumer crops*

An important factor is a distance from external sources of contamination represented by consumer potato plots and regrowth in other crops. It may be interesting to exclude some crops from plant production areas as they may be a source of vector aphids. The standards for isolation are:


#### *3.3.1.4 Severe mass selection or varietal treatment in propagating crops*

Selection is mandatory from the beginning of the vegetation until the beginning of yellowing of the leaves (early maturity).

It consists of the removal of foreign and nonconforming plants, regrowth and plant with virus diseases as soon as symptoms appear, severe rhizoctonia and verticillium.

### *3.3.1.5 Early dehaulming to remove leaves from plants and prevent them to infections*

Potato plots are systematically removed early, meaning that the foliage is reduced before ripening. This practice removes vegetation from aphid flight and prevents virus migration to the tubers (in the case of late contamination). The follow-up of aphids allows knowing whether or not to advance the dates of dehaulming.

By limiting the life of the foliage, removing old leaves also helps to limit the growth of the tubers. This is one of the ways to obtain a suitable proportion of small and medium-size tubers corresponding to the regulation of plant trade.

#### *3.3.2 Pre-base seed production*

#### *3.3.2.1 Production of quality plants by in vitro micropropagation*

In the in vitro system, parts of plants are propagated and regenerated into whole plants or tubers under sterile artificial conditions. For rapid multiplication, three types of material can be used: (a) Node cuttings, (b) Apical cuttings and (c) Micro-tubers [14]

Apical cuttings are not frequently used because they are not widely available. To do this, we will focus our attention on node cuttings and micro-tubers.

#### *3.3.2.1.1 Node cuttings*

When a large quantity of seedlings with high genetic quality and a maximum sanitary condition is desired, rapid multiplication is done by node cutting. The various steps are as follows:

#### **1. Source plant selection and treatment**

Three types of plant material are used:

• Tubers; where the tubers are used as starting material, they must first be pregerminated, after which the buds are harvested. This step can take 2 months.


These materials must conform to the cultivar and be viral tested (mainly PVX, PVS, PVY, PVA, PVM, and PLRV), bacteria (stem rot, brown rot and those caused by Erwinia spp) and other diseases.
