A New Stem-splitting Symptom in Safflower Caused by Macrophomina phaseolina

Safflower is known to be attacked by several seedborne fungi, of which Macrophomina phaseolina is one of the most important pathogens causing serious yield losses. During routine experiments, a new stem-split symptom was observed in M. phaseolina-infected plants resulting in poor growth and reduced size of inflorescences. Stem-split was observed in 30-day-old plants as minute cracks approximately 2–3 cm above the soil surface, which over time extended to both upward and downward directions, resulting in the formation of a wider split. The split portion was hollow and brown with a white to grey mycelial mat of the fungus on the inner surface. Such plants became lodged, ultimately resulting in poor seed yield compared with healthy plants. The stem-split plants showed delayed flowering by 1 week over healthy plants. One of the three M. phaseolina isolates used for inoculation of seeds and plants was more aggressive but all isolates were able to reproduce the stem-split symptoms found on naturally infected safflower plants in the field