New Delhi, Jan 2 (ESPN): India team director Ravi Shastri is "bullish" about the Test side's future, saying that the key was to develop an attack that could take 20 wickets on a regular basis. The deciding factor in the ongoing four-Test series, which Australia won after maintaining their 2-0 lead by drawing the third Test at the MCG, according to Shastri, was the difference between the bowling groups: Australia's had experience and India's did not.

"There's hard work ahead no doubt," Shastri said. "Primarily, we have to get or develop bowlers who can get 20 wickets regularly. But I am extremely bullish. The most important thing is we have got an aggressive mindset. Let's talk 12-15 months down the road."

India will be led by Virat Kohli in the final Test in Sydney, following MS Dhoni's sudden retirement from Test cricket at the end of the third match in Melbourne, a development Shastri said had left the dressing-room "stumped". However, he said the change in leadership was unlikely to affect the players' mindsets.

"In my days, I played under several captains, none of whom were alike," Shastri said. "Captains have their own personalities and the best ones make players adapt to their thinking and methods."

Kohli has been in the news on this tour not only for the runs he has made, but also for his aggressive behaviour on the field and a confrontational press conference in Melbourne, where he said he did not respect all the Australian players. Shastri backed Kohli, despite the results not falling India's way.

"That's his personality," Shastri said when asked if Kohli's comments, especially those on Mitchell Johnson, had been unnecessarily provocative. "He is aggressive, passionate and wears his heart on his sleeve. But he's also prepared to walk the talk. Remember also, he's only 26 and still getting used to captaincy. With a little luck, the score line could well have been different. This is a young team that has acquitted itself very creditably."

Shastri squashed reports suggesting Dhoni's retirement could have been precipitated by the rising influence of Kohli in the dressing room, saying such speculation was "trash".

"You guys have no idea of the respect Dhoni commands," Shastri said, "not just from Virat but every member of the squad, support staff and administration.

When asked if he had an inkling of Dhoni's retirement, Shastri said: "None. It came like a bolt from the blue. Not till after he returned from the post-match presentation did I come to know when he had a quick word with me, then the players. I understand he had not even spoken to his family about it.

"It was an unexpected decision no doubt, but a courageous one. In my esteem Dhoni has gone up by miles. He hasn't waited to complete 100 Tests and all such pointless statistical stuff. He didn't want any farewell fanfare. That shows his character. He's different and quite remarkable."