Banana fruit fingers not filling, leaves yellowing between veins (kela)

Poorly filled, thin fruit fingers together with yellowing between the leaf veins most often point to a nutrient problem rather than a pest or virus, commonly a shortage of potassium, magnesium or other elements, since banana is a heavy feeder that needs a lot of potassium to fill the bunch. Yellowing between the veins while the veins stay green is a typical deficiency pattern, but the exact element should be confirmed by a soil or leaf test through your KVK, because magnesium, potassium and other deficiencies look slightly different and over-fertilising the wrong one wastes money. It is also worth ruling out root damage, waterlogging or nematodes that stop the plant taking up nutrients, and checking that the plant is well watered, since water stress at bunch stage gives thin fingers too. Once the deficiency is confirmed, correct it with the right fertiliser dose and timing your KVK recommends, applied in splits, and consider foliar feeding for a quick correction if advised. Keep irrigation steady through bunch development. Get the soil and leaf tested before buying inputs, so you feed the actual shortage.