Micropropagation of "Wild pear" Pyrus pyrifolia (Burm F.) Nakai. II. Induction of Rooting

The present study was undertaken to study the effects of cultural conditions, auxins and phloroglucinol on in vitro rhizogenesis in wild pear. Higher mean rooting percentage (28.78%) was obtained in solid medium, as compared to liquid medium (6.80%), irrespective of the growth regulator concentrations used. The rooting response was better with lower concentrations (0.125 and 0.25 mg l-1) of NAA than IBA. At higher growth regulator concentrations (0.5-2.0 mg l-1) though the rooting response was poor, yet significantly higher rooting was observed with IBA as compared to NAA. A combination of NAA and IBA resulted in significant improvement of rooting percentages over NAA or IBA alone. However, this improvement in rooting response was only at lower concentrations (0.125 and 0.25 mg l-1) of auxin combination (NAA+IBA). The highest rooting (81.47%) was obtained on solid medium with NAA and IBA at 0.25 mg l-1 each followed by NAA and IBA 0.125 mg l-1 each (78.24%). 2,4-D failed to induce rooting. A higher number of roots (2.53) was obtained on solid medium, than on liquid medium (1.48). NAA resulted in higher number of roots per shoot than IBA, but at lower concentrations viz. 0.125-0.25 mg l-1. The highest number of roots per microshoot (7.20) was obtained on liquid medium supplemented with NAA (0.25 mg l-1). It was on a par with NAA + IBA (0.25 mg l-1 each) and IBA 0.25 mg l-1. However, the latter treatments resulted in low rooting percentages and very poor root length. The root length in solid medium (1.18 cm) was significantly more than that on liquid medium. During the in vitro root induction some microshoots died of shoot-tip necrosis (STN). The STN percentages were significantly reduced on liquid medium in comparison to solid medium. Raising the Ca levels to 3 mM (T1) significantly reduced the STN (2.60%). However, a further increase in Ca levels to 6 and 9 mM considerably increased the STN. The boron supplementations (200, 500 and1000 microM) reduced the STN to zero per cent and no symptoms of boron toxicity was observed even at 1000 microM. Rooting behaviour of the wild pear was significantly affected by the media phase and phloroglucinol. PG had a stimulatory effect on the rooting response of wild pear and the roots obtained on solid medium supplemented with PG were better than those on liquid medium. The highest ex vitro survival percentage of the wild pear plantlets (52.03 %) was observed on sand + soil (3:1 v/v) followed by 33.77 % on sand + soil (2:1 v/v) and 10.50% on perlite.