Learning to reason agro-ecologically to design and manage more efficient, productive, profitable and clean Musa production

Musa growth cycle and productivity – importance of temperature, water, light, and nutrients

Mother plant with follower sucker (daughter) and small peeper (granddaughter
Growth of a banana plant from the growing point or meristem

A farmer begins a new field of banana or plantain by planting either suckers from another banana field or young plants produced by tissue culture. Each new stem produces only one bunch, but numerous lateral shoots that become the next generation of bunches each from its own stem. In time the lateral shoots produce their own lateral shoots which produce bunches, each from its own stem. The stem bearing the bunch is cut down when the bunch is harvested. The parent plant and the successive lateral shoots are referred to as a stool or mat. Let’s look at the key events in the life cycle of a banana mat to understand how we can get more and better bunches from our field.

How many leaves per stem?
Each sucker or new plant has a growing point where the new leaves, flowers and fingers originate. This growing point can be found in the center of the corm just above ground level where the leaf sheaths are attached.

The growing point produces between 30 to 50 leaves. Shorter cultivars are generally characterized by the production of fewer total leaves, while taller cultivars produce more total leaves before flowering. Within a cultivar, the total number of leaves is very similar from stem to stem and mat to mat. The first leaves are small and may even be hard to see. During early growth each leaf is bigger than the previous one. New leaves emerge from the center of older leaves. The leaf sheaths are tightly wrapped to form the trunk or pseudostem which becomes taller and taller during the first few months.

New leaves develop above older leaves and a healthy plant may have between 10-15 active leaves at any one time. Once the plant has produced 30-50 leaves, the flower bud is formed. No more leaves can be produced after that. When the flower bud is formed, there are 11 leaves within the stem remaining to emerge.

How fast does a stem produce a bunch?
Under optimal growing conditions (temperature, water, light, nutrients, soil), a new leaf emerges every 6-8 days. If the plant has optimum conditions, the time from the first leaf to the last leaf will be 245 to 320 days (8 to 11 months). However, when we plant a sucker or a tissue culture plant, they already have produced some leaves. Small suckers have produced fewer leaves up to the point of planting, while larger suckers have produced more leaves and therefore produce fewer leaves after planting until flowering. This is only true if primary growing point of the sucker forms the new plant. If a small lateral bud on the sucker becomes the main stem, it has more potential leaves before flowering. Under optimum field conditions the time period from planting until the last leaf is formed may only be 180 to 250 days (6 to 8 months). When conditions are less than optimum, leaf emergence is slower. However, the total number of leaves to emerge until flowering remains within a certain range. Therefore, the time to last leaf emergence becomes longer and may reach up to 500 days (16 months) in subtropical regions.

At the time of planting, some suckers have produced more leaves than others. Therefore, they have fewer leaves to produce until harvest. However, a lateral bud may also sprout which has many potential leaves until harvest.
To calculate the time from planting to bunch harvest, we also need to consider the time for the flowers to become fully developed fruits. This will take from 90 to 220 days (3 to 7 months), depending on growing conditions and the variety.

Do all leaves emerge at the same interval?
Although we have said that leaves emerge every 6-8 days under optimum conditions, if you stand by a banana stem and count the days from one leaf to the next, you will discover that younger leaves emerge faster. Under optimum conditions, the very first leaves emerge every four days and interval becomes progressively long until the last leaves to emerge take seven to 10 days for each leaf.

Interval for leaf emergence under optimal conditions for        
Leaves 1-10                        4,3 days = 43 days
Leaves 11-20                      5,4 days = 54 days
Leaves 21-30                      6,5 days = 65 days
Leaves 31-40                      7,6 days = 76 days
Total days                            = 238 days (8 months)
Days per leaf                       = 6 days

Bunch size
Bunch size is determined by the number of fruit on the bunch and the size of those fruit. The number of fruit on the bunch is determined before the bunch emerges from top of the pseudostem. The size of the last few leaves that emerge indicates the number of fruit on the bunch. This means that plants which are growing vigorously enough to produce big leaves before flowering will produce bigger bunches. Water and nutrient stresses reduce leaf size and therefore the number of fingers in the bunch. This is why the number of leaves at flowering is an important indicator of plant productivity. A plant with 10 healthy leaves at flowering will produce a bigger bunch than a plant with only 5 healthy leaves.
The size of the fruit is determined to some extent by conditions just before emergence, but mostly by the conditions after emergence. This is why the number of healthy leaves is an important indicator of bunch size. The number of fruit on the bunch and their size can compensate for one another to some extent. Fruit size is often a measure of quality in the market. The last hands may be pruned at flowering so that the remaining fruit can grow large enough to meet the requirements of consumers. This is not a problem if consumers like small bananas.

How long from one generations of bunches to the next?
When does the parent plant generate lateral buds on the corm that grow into new shoots? This is an important factor in field productivity, since it strongly influences the time interval between the first generation of bunches and the next generation of bunches. In some types of Musa such as plantain, lateral buds are released for growth when the flower bud is initiated in the parent corm. Remember that we said that 11 leaves remain with the stem to emerge when the flower is initiated. Since this is the moment when lateral shoot growth begins, this means that overlap between the growth of the parent stem and the growth of the next generation, called the ratoon crop, is the time for the emergence of 11 leaves and the time for bunch formation. As a result, the interval from the harvest of the first bunch and the harvest of the second bunch may be as short as 180 days (6 months). In other cultivars, the production of new lateral shoots is not closely linked to flower initiation. Lateral shoots may be produced before flower initiation and continue afterwards. Lateral shoots are not usually produced on a parent after its bunch has emerged from the top of the pseudostem.

How do the roots grow?
The root system is equally important for productivity. Bananas and plantains have a root system made up of many, many roots arising from the corm. These cord roots emerge from interior layers of the corm. They have a diameter of 5-10 mm like a thin pencil and are characterized by a growing tip, a zone of root hairs from 4-12 cm from the tip and then a zone from which secondary roots arise about 12 - 15 cm from the tip. Secondary roots are much thinner than the primary cord roots. If the growing tip is damaged or cut, lateral root formation can compensate. However, if damage occurs more than 20 cm from the tip, growth ceases and the root even loses the potential to generate secondary roots.

When a sucker is planted, roots already initiated emerge in a first flush and may reach 40 cm before leaves begin to emerge. The next flush of roots is delayed for several weeks. A cord root grows up to 2 cm per day. A healthy corm has as many as 200-300 primary cord roots, totaling more than 200 meters of roots, an average of 1 meter per root. These roots are concentrated in the upper 30 cm with more than 80% of roots in upper 60 cm. Once flowering is initiated, new root emergence from the corm stops, although existing roots continue to function. However, the lateral stems continue to produce roots. The root system of the mat consists of the roots from the mother stem and the roots being formed by the lateral shoots. Most roots are concentrated in a zone 60 – 100 cm from the base, but often extend beyond 2 meters.

Are bigger bunches enough?
We are all impressed by reports of 50 kg bunches with over 150 fingers and we imagine a highly productive banana field. However, from the information we have just reviewed, it is clear that many more factors are important in the total productivity of a banana field. Of equal importance is the number of bunches produced in a given area of land over a given period of time. In addition, we need to know how many plants there are per land area. We also need to know the rate of production. As we have seen above, the rate of production depends on the total leaves which a stem produces, the rate of leaf production and the point in the parent plant cycle when the lateral shoot is produced. Some of these factors depend on cultivar, while others are influenced by growing conditions.
Viewed in this way, the major focus is bananas produced per land area per time. However, if labor costs are important, we may also want to look at production per unit of labor. Similarly, the grower may have limited capital to invest and analyzes production per cash invested. In many areas, bananas and plantains are associated with other crops. The changes in productivity of one crop must be balanced with possible productivity losses or gains in the other crops.

Which is more productive? To decide, we need to think about the farm household objectives and the resources available, especially for food security and poverty reduction.