It is Yellow Mosaic Disease. It spreads from infected plants and sometimes through carrier sucking pests like aphids. There is no cure, but affected leaves should be removed. You can try a natural remedy: wood ash in water overnight, then collect the clear water from the top and spray it on the plants.

Control sucking pests by spraying insecticides throughout the plant every 7 days. If yellowing plants do not recover and do not produce as much, apply potassium-rich fertilizers to make them healthier.