Factors Affecting the Growth of Cordyceps militaris

1. Nutritional Factors

(1) Carbon Source

As the foundation for synthesizing carbohydrates and amino acids as well as a critical energy source, carbon sources play a vital role for Cordyceps militaris. For artificial cultivation, usable carbon sources include glucose, sucrose and starch. Small‑molecule saccharides such as glucose deliver the best utilization performance.

(2) Nitrogen Source

Nitrogen sources are essential for Cordyceps militaris to synthesize protein and nucleic acid. Usable organic nitrogen sources comprise yeast extract, beef extract, amino acids, peptone, soybean meal, corn flour and silkworm pupa powder. Major inorganic nitrogen sources include ammonium chloride and sodium nitrate. Organic nitrogen shows superior utilization effect. Insufficient nitrogen leads to slow fruiting‑body emergence and low yield. Excessive nitrogen triggers over‑vigorous aerial mycelium and inhibits fruiting‑body initiation. Even if primordia form, both quantity and quality of fruiting bodies will decline.

(3) Mineral Substances

Cordyceps militaris requires minerals including phosphorus, potassium, sulfur, calcium, magnesium, germanium and selenium for growth and development. Common mineral supplements are calcium carbonate, magnesium sulfate, potassium dihydrogen phosphate and gypsum.

(4) Vitamins

Growth factors such as vitamins are required by Cordyceps militaris. Since it cannot synthesize B‑group vitamins by itself, Vitamin B₁ and Vitamin B₂ are commonly supplemented in cultivation substrates.

Proper carbon‑nitrogen ratio (C/N) is indispensable for artificial cultivation to optimize growth rate, yield and quality. Improper C/N ratio may cause slow mycelial growth, high contamination risk, exuberant aerial mycelium and poor fruiting‑body formation, resulting in reduced yield and quality. For most fungi, mycelial‑stage C/N ratio stands at 25‑30:1. Cordyceps militaris demands higher nitrogen input: the optimal C/N ratio is 4‑6:1 for vegetative growth phase, and 10‑15:1 for reproductive growth phase.

2. Environmental Conditions

(1) Temperature

Cordyceps militaris is a mesophilic fungus requiring temperature fluctuation for fruiting‑body formation.

• Mycelial growth: 5‑30 °C, optimum 18‑23 °C
• Primordia differentiation: 15‑25 °C; a temperature difference of 5‑8 °C effectively stimulates primordium initiation
• Fruiting‑body development: 10‑25 °C, optimum 18‑22 °C

Temperatures above 10 °C but relatively low only extend production cycles. Temperatures over 25 °C shorten cultivation cycles yet raise contamination rate and degrade product quality.

(2) Humidity

Suitable substrate moisture content for normal growth is 60%‑65%. Below 50%, mycelia grow slowly, turn thin, yellow, brittle and may even die. Excessively high moisture turns substrate pasty after sterilization and hinders internal mycelial penetration, bringing dense surface mycelium, pigment accumulation on bottle walls, poor sexual reproduction and substrate acidification. During spawn‑running stage, relative air humidity of cultivation room shall be maintained at 60%‑65%. For primordia formation and fruiting‑body growth, keep air relative humidity at 85%‑90% to realize fast‑growing and dense fruiting‑body clusters. After harvesting the second batch of fruiting bodies, substrate moisture drops to 45%‑50%. Nutrient solution irrigation is recommended for moisture and nutrient replenishment between flushes.

(3) Light

Mycelial growth does not require light. Light inhibits mycelial development, darkens substrates, induces abundant aerial mycelium and accelerates pellicle formation. Proper diffused light is necessary for primordia differentiation. Insufficient light causes sparse primordia; uneven light leads to distorted or skewed fruiting bodies; prolonged continuous lighting suppresses fruiting‑body formation. During fruiting‑body stage, provide intermittent diffused light of 200‑500 lx daily. Weak light produces pale‑yellow, low‑yield fruiting bodies; moderate light guarantees favorable color, high yield and good quality; excessive light causes premature maturation of fruiting bodies.

(4) Air

Cordyceps militaris is an aerobic fungus with oxygen‑consuming and carbon‑dioxide‑releasing metabolism. Oxygen demand surges after primordia emerge, hence fresh air supply is critical. Poor ventilation combined with high humidity restrains mycelial growth and facilitates contaminant mould proliferation. During primordia differentiation, insufficient ventilation impedes colour transition, delays fruiting‑body emergence and triggers excessive branching. High CO₂ concentration during fruiting‑body period results in dense, slender malformed fruiting bodies.

(5) pH Value

Cordyceps militaris prefers slightly‑acidic environment. Mycelia survive within pH 5.0‑8.0, with optimum pH 5.5‑6.5. The optimal pH for fruiting‑body growth is 6.0. pH value tends to decrease during sterilization and cultivation. Therefore initial substrate pH should be adjusted 1 unit higher. After autoclaving and organic‑acid secretion by mycelia, substrate pH naturally falls to around 6.0. Add 0.1%‑0.2% potassium dihydrogen phosphate as buffer to stabilize substrate pH.